Synthesis, spectroscopic properties and structural characterisation of Pd(II) and Pt(II) complexes with 1,3,5-pyrazole derived ligands. Rotation around the metal-N bond

Reactions of ligands 1-ethyl-5-methyl-3-phenyl-1H-pyrazole (L¹) and 5-methyl-1-octyl-3-phenyl-1H-pyrazole (L²) with [PdCl₂(CH₃CN)₂ and K₂PtCl₄ gave complexes trans-[MCl₂(L)₂] (L = L¹, L²). The new complexes were characterised by elemental analyses, conductivity measurements, infrared, ¹H and ¹³C{¹H} NMR spectroscopies and X-ray diffraction. The NMR study of the complex [PdCl₂(L¹)₂], in CDCl₃ solution, is consistent with a very slow rotation of ligands around the Pd-N bond, so that two conformational isomers can be observed in solution (syn and anti). Different behaviour is observed for complexes [PdCl₂(L²)₂] and [PtCl₂(L)₂] (L = L¹, L²), which present an isomer in solution at room temperature (anti). The crystal structure of [PdCl₂(L¹)₂] complex is described, where the Pd(II) presents a square planar geometry with the ligands coordinated in a trans disposition.     

The platinum complexes with histamine: Pt(II)(Hist)Cl2, Pt(II)(Iodo-Hist)Cl2 and Pt(IV)(Hist)2Cl2

The Pt(II) and Pt(IV) complexes with histamine were calculated by using more than 20 DFT functionals and various basis sets. Based on the comparison between the X-ray and theoretical geometrical parameters of the Pt(II)(Hist)Cl₂ complex the MPW1PW91, OPW91 and SVWN5 functionals combined with the 6-311G^∗∗ basis set for non-metallic and SDD (ECP) basis set for platinum were found to yield the most satisfactory agreement. The structure of the Pt(II) complex with iodohistamine important for pharmacy, so far isolated only in minute amounts, was predicted by using the MPW1PW91 functional. Comparison of the theoretical NMR chemical shifts of the Pt(II)(Hist)Cl₂ complex with those found experimentally have shown that the theoretical ¹H and ¹³C NMR chemical shifts are in plausible agreement with the experimental ones, whereas the theoretical ¹⁹⁵Pt chemical shifts fit the experimental values only when the relativistic approach is applied within the ZORA formalism. We confirmed suitability of the three selected functionals for reproduction of the experimental structure of Pt complexes at fourth oxidation state by using the cis- and ions as models. Finally, with the selected theoretical methods, the structures and stabilities of four Pt(IV)(Hist)₂Cl₂ complex isomers were predicted.     

Platinum(II) complexes with l-methionylglycine and l-methionyl-l-leucine ligands: synthesis, characterization and in vitro antitumoral activity

Four dipeptide complexes of the type [PtX(2)(dipeptide)] x H(2)O (X=Cl, I, dipeptide=l-methionylglycine, l-methionyl-l-leucine) were prepared. The complexes were characterized by (1)H, (13)C, (195)Pt NMR and infrared spectroscopy, DTG and elemental analysis. From the infrared, (1)H and (13)C NMR spectroscopy it was concluded that dipeptides coordinate bidentately via sulfur and amine nitrogen donor atoms. Confirmed with (13)C and (195)Pt NMR spectroscopy, each of the complexes exists in two diastereoisomeric forms, which are related by inversion of configuration at the sulfur atom. The (1)H NMR spectrum for the platinum(II) complex with l-methionylglycine and chloro ligands exhibited reversible, intramolecular inversion of configuration at the S atom; DeltaG( not equal)=72 kJ mol(-1) at coalescence temperature 349 K was calculated. In vitro cytotoxicity studies using the human tumor cell lines liposarcoma, lung carcinoma A549 and melanoma 518A2 revealed considerable activity of the platinum(II) complex with l-methionylglycine and chloro ligands. Further in vitro cytotoxic evaluation using human testicular germ cell tumor cell lines 1411HP and H12.1 and colon carcinoma cell line DLD-1 showed moderate cytotoxic activity for all platinum(II) complexes only in the cisplatin-sensitive cell line H12.1. Platinum uptake studies using atomic absorption spectroscopy indicated no relationship between uptake and activity. Potential antitumoral activity of this class of platinum(II) complexes is dependent on the kind of ligands as well as on tumor cell type.     

Electrochemical and spectroscopic evidences of the interaction between DNA and Pt(II)(dppf)-complex

The interaction of Pt(II)(dppf)-complex, namely [Pt(dppf)(H₂O)₂]²⁺ with DNA was investigated by DPV and ¹H-NMR techniques. The results showed that the interaction process has been characterized by changes in the electrochemical parameters of both compounds and the formation of a new anodic current peak close to the anodic current peak of the [Pt(dppf)(H₂O)₂]²⁺. In addition, the ¹H-NMR spectra show that the coordination of Pt(II)(dppf)-complex to dsDNA occurs via N(7) of guanine. Others parameters like pH and ionic strength that affect the interaction process were also investigated.     

Crystal structures of Pt(II) and Pd(II) complexes with the free radical 4-aminoTEMPO

Pt(II) and Pd(II) compounds containing the free radical 4-aminoTEMPO (4amTEMPO) were synthesized and characterised by X-ray diffraction methods. The disubstituted complexes cis- and trans-Pt(4amTEMPO)₂I₂ were studied. The trans isomer was prepared from the isomerisation of the cis analogue. The two Pd(II) compounds trans-Pd(4amTEMPO)₂X₂ (X = Cl and I) were also characterised by crystallographic methods. A mixed-ligand complex cis-Pt(DMSO)(4amTEMPO)Cl₂ was synthesized from the isomerisation of the trans isomer in hot water. Its crystal structure was also determined. In all the complexes, the 4amTEMPO ligand is bonded to the metal through the -NH₂ group, since the nitroxide O atom is not a good donor atom for the soft Pt(II) and Pd(II) metals. The conformation of the 4-aminoTEMPO ligand was compared to those of the few reported structures in the literature.     

Synthesis and reactivity of diphosphino Pt(II) silanolate complexes as molecular models of the interaction of platinum particles with silica

A series of di- and monosubstituted cis-platinum(II) silanolate complexes, Pt(OSiR₃)₂(dppe) (R=Et, 1; R=Me, 2) and Pt(OSiR₃)Cl(dppe) (R=Et, 3; R=ⁱPr, 4) where dppe is 1,2-bis(diphenylphosphino)ethane, have been isolated and characterised spectroscopically. Complex 1 does not react with CO and H₂ under anhydrous conditions, but the complexes Pt{C(O)OCH₃)}₂(dppe) (6) and Pt(CO₃)(dppe) (7) have been isolated bubbling CO in methanol and CO₂ in moist benzene solutions of 1, respectively. The behaviour of 1 towards water or methanol is discussed on the basis of ¹H, and ³¹P{¹H} NMR spectroscopic data. The new complex Pt{S₂C(OSiEt₃)₂}(dppe) (8) has been isolated by reaction of 1 with CS₂ in benzene solution. This reactivity would suggest a high sensitivity towards water, but not towards H₂ or CO, of the bonding of slightly oxidised platinum particles with silanol groups of silica surface.     

Cellular accumulation and DNA platination of two new platinum(II) anticancer compounds based on anthracene derivatives as carrier ligands

The anticancer properties of two new fluorescent platinum(II) compounds, cis-[Pt(A9opy)Cl₂] and cis-[Pt(A9pyp)(dmso)Cl₂] are described. These compounds are highly active against several human tumor cell lines, including human ovarian carcinoma sensitive and cisplatin-resistant cell lines (A2780 and A2780R). To study the cellular processing of these new compounds, a series of in vitro studies have been performed, including the investigation of intracellular platinum accumulation and DNA-platination experiments in A2780 and A2780R cells. Compared to cisplatin, both compounds are accumulated highly in both sensitive and resistant cell lines, and more platinum has been found to bind to the nuclear DNA. Interestingly, cis-[Pt(A9opy)Cl₂] shows high accumulation and DNA adduct formation in the resistant cell line A2780R, as compared to the sensitive counterpart A2780 cell line. This suggests that cis-[Pt(A9opy)Cl₂] is able to overcome some of the well-known resistance mechanisms in this cell line, such as decreased cellular uptake and increased DNA repair.     

Terpene conjugates of diaminedichloridoplatinum(II) complexes: antiproliferative effects in HL-60 leukemia, 518A2 melanoma, and HT-29 colon cancer cells

Twenty-eight [6-(aminomethyl)nicotinate]dichloridoplatinum(II) complexes 1 esterified with various terpene alcohols either directly or via alkyl spacers were tested for antiproliferative activity in human 518A2 melanoma and HL-60 leukemia cells. Generally, conjugates with menthanes and polycyclic sesquiterpenes attached via propane-1,2-diyl spacers were most active. In the melanoma cells, the propane-1,2-diyl-spacered conjugates of (-)-menthol (1a(2')), (+)-neomenthol (1b(2')), (-)-carvomenthol (1h(2')), and (-)-isolongifolol (1n(2')) displayed growth inhibition at IC(50)<4 microM which is ten times smaller than that of cisplatin. The stationary diamino ligand was also crucial. The (-)-menthyl ester complexes with 2,3-diaminopropanoate (9a) and 2,4-diaminobutanoate (10a) ligands caused a greater and persistent growth inhibition in HT-29 colon cancer cells upon long-term exposure when compared to the 6-(aminomethyl)nicotinate analogue 1a. The cedrenyl ester 1l and the menthoxyisopropyl ester 1a(2') proved most efficacious in all three tumor cell lines. The DNA binding of complexes 1 was assessed by electrophoretic band-shift experiments and found correlated to the terpene structure but not to the observed antiproliferative activities.     

New Pd(II) and Pt(II) complexes with N,S-chelated pyrazolonate ligands: molecular and supramolecular structure and preliminary study of their in vitro antitumoral activity

New Pd(II) and Pt(II) complexes [ML2] (HL=a substituted 2,5-dihydro-5-oxo-1H-pyrazolone-1-carbothioamide) have been synthesized by reacting K2MCl4 (M=Pd, Pt) or Pd(OAc)2 with beta-ketoester thiosemicarbazones. The structures of seven of these complexes were determined by X-ray diffraction. Although all exhibit a distorted square-planar coordination with trans- or (in one case) cis-[MN2S2] kernels, their supramolecular arrangements vary widely from isolated molecules to 3D-networks. The in vitro antitumoral assays performed with two HL ligands and their metal complexes showed significant cytostatic activity for the latter, with the most active [ML2] derivative (a palladium complex) being about sixteen times more active than cis-DDP against the cisplatinum-resistant cell line A2780cisR.     

DNA interaction and antiproliferative behavior of the water soluble platinum supramolecular squares [(en)Pt(N-N)]4(NO3)8 (en=ethylenediamine, N-N=4,4'-bipyridine or 1,4-bis(4-pyridyl)tetrafluorobenzene)

The interaction with DNA of two water soluble platinum supramolecular squares [(en)Pt(N-N)]4(NO3)8 (en=ethylenediamine, N-N=1,4-bis(4-pyridyl)tetrafluorobenzene, compound 1, N-N=4,4'-bipyridine, compound 2) has been studied by circular dichroism, electrophoretic mobility and atomic force microscopy. the two complexes drastically modify the second and tertiary structures of DNA, but compound 2 does it strongly due probably to its smaller size by comparison with compound 1 and its more suitable structural features for intercalation between base pairs. The two supramolecular squares were assayed against the HL-60 tumor cell line for 24 and 72 h. The IC50 values for 24 h are smaller than that of cisplatin for this time, however for 72 h the IC50 have higher values being the corresponding to compound 2 comparable to that of cisplatin. Apoptotic assays were also carried out for the compounds 1 and 2 against the tumor cell line.     

Mono- and polynuclear complexes of Pt(II) with polypyridyl ligands. Synthesis, spectroscopic and structural characterization and cytotoxic activity

An array of poly- and mononuclear complexes of Pt(II) with polypyridyl ligands is reported. The framework complexes [(PtCl(2))(2)(bpp)(2)(micro-PtCl(2))](H(2)O)(2) [bpp=2,3-bis(2-pyridyl)pyrazine], [PtCl(2)(micro-tptz)PtClNCPh]Cl [tptz=2,4,6-tris(2-pyridyl)-1,3,5-triazine], and mononuclear PtCl(2)(NH(2)dpt) [NH(2)dpt=4-amino-3,5-bis(2-pyridyl)-1,2,4-triazole] have been prepared and structurally characterized. Both neutral and ionic complexes are present, with bifunctional and monofunctional Pt(II) moieties, whose size and shape enable them to behave as novel scaffolds for DNA binding. Pt(II) complexes were tested for their biological activity. Cell viability assay and flow cytometric analysis demonstrated that these complexes, particularly [PtCl(2)(micro-tptz)PtClNCPh]Cl, were effective death inducers in human colon rectal carcinoma HT29 cells and their cytotoxic activity was higher than that exerted by cisplatin. Morphological analysis of treated HT29 cells, performed by fluorescence microscopy after Hoechst 33258 staining, showed the appearance of the typical features of apoptosis. Moreover, our results suggested that mitochondria are involved in apoptosis induced by Pt(II) complexes in HT29 cells as demonstrated by dissipation of mitochondrial transmembrane potential.     

The microwave synthesis of platinum(II) phosphine complexes

The microwave synthesis of a series of platinum(II) phosphine complexes is reported. The complexes dppePtCl₂ (dppe = bis(diphenylphosphino)ethane), dpppPtCl₂ (dppp = bis(diphenylphosphino)propane), dppmPtCl₂ (dppm = bis(diphenylphosphino)methane) and cis-(Ph₃P)₂PtCl₂ are synthesized from the reaction of potassium tetrachloroplatinate(II) and the phosphine. The isolated yields are 65% or better.     

Synthesis and characterisation of new N1-alkyl-3,5-dipyridylpyrazole derived ligands. Study of their reactivity with Pd(II) and Pt(II)

Two new pyrazole-derived ligands, 1-ethyl-3,5-bis(2-pyridyl)pyrazole (L¹) and 1-octyl-3,5-bis(2-pyridyl)pyrazole (L²), both containing alkyl groups at position 1 were prepared by reaction between 3,5-bis(2-pyridyl) pyrazole and the appropriate bromoalkane in toluene using sodium ethoxide as base.The reaction between L¹, L² and [MCl₂(CH₃CN)₂] (M = Pd(II), Pt(II)) resulted in the formation complexes of formula [MCl₂(L)] (M = Pd(II), L = L¹ (1); M = Pd(II), L = L² (2); M = Pt(II), L = L¹ (3); M = Pt(II), L = L² (4)). These complexes were characterised by elemental analyses, conductivity measurements, infrared, ¹H, ¹³C{¹H} NMR and HMQC spectroscopies. The X-ray structure of the complex [PtCl₂(L²)] (4) was determined. In this complex, Npyridine and Npyrazole donor atoms coordinate the ligand to the metal, which complete its coordination with two chloro ligands in a cis disposition.     

Synthesis, spectroscopy, structure and photophysical properties of dinaphthylmethylarsine complexes of palladium(II) and platinum(II)

Dinaphthylmethylarsine complexes of palladium(II) and platinum(II) with the formulae [MX₂L₂] (M = Pd, Pt; L = di(1-naphthyl)methylarsine = Nap₂AsMe and X = Cl, Br, I), [M₂Cl₂(μ-Cl)₂L₂], [PdCl(S₂CNEt₂)L], [Pd₂Cl₂(μ-OAc)₂L₂] and [MCl₂(PR₃)L] (PR₃ = PEt₃, PPr₃, PBu₃, PMePh₂) have been prepared. These complexes have been characterized by elemental analyses, IR, Raman, NMR (¹H, ¹³C, ³¹P) and UV-vis spectroscopy. The stereochemistry of the complexes has been deduced from the spectroscopic data. The crystal structures of trans-[PdCl₂(PEt₃)(Nap₂AsMe)] and of [Pd(S₂CNEt₂)₂], a follow-up product, were determined. The UV-vis spectra of [MX₂L₂] complexes show a red shift on going from X = Cl to X = I. The complexes [PdX₂L₂] and [PtX₂L₂] are strongly luminescent in fluid solution and in the solid at ambient temperature.     

Steric influence on platinum(II) ascorbate complexes

From the reaction between dihydroxoplatinum(II) and l-ascorbic acid, two types of platinum(II) ascorbate complexes were obtained and structurally characterized with ethylenediamine (en), N,N-dimethylethylenediamine (dmen) and N,N,N′-trimethylethylenediamine (trimen) as stabilizing ligands. In [Pt(en)(asc-C,O)] (1), [Pt(dmen)(asc-C,O)] (2) and [Pt(trimen)(asc-C,O)] (4), the ascorbate dianion forms a five-membered chelate ring, coordinating to the Pt(II) ion at the 2-carbon and the 5-oxygen atoms (C,O-chelate). From the same mother solution, crystals of [Pt(trimen)(asc-O,O′)] (3) were obtained during the precipitation of 4; in 3 the ascorbate is bound to the Pt at the 2- and 3-oxygen atoms (O,O′-chelate). Compounds 3 and 4 are the first well-characterized linkage isomers among the transition-metal ascorbate complexes. The O,O′-chelated 3 slowly changes to the C,O-chelated 4 in an aqueous solution. Bulkiness of the stabilizing ligand, i.e. en, dmen and trimen has an influence on the formation of the C,O-chelated species, 1, 2 and 4.     

Water soluble platinum(II) and palladium(II) complexes of alkyl sulfonated phosphines

The reactions of the alkylsulfonated phosphines LM=Ph₂P(CH₂)_nSO₃Na/K (n=2, 3, 4) with K₂PtCl₄ and K₂PdCl₄ have been studied in homogeneous aqueous solution as a function of pH. In homogeneous acidic solution the protonated phosphines react to give cis- and trans-PtCl₂(LH)₂. The biphasic reaction between 1,5-cyclooctadiene platinum(II) chloride in dichloromethane and acidified aqueous LNa/K gives a higher proportion of the cis isomer. In neutral solution the initial reaction to give [PtCl(LNa/K)₃]⁺Cl⁻ is followed by slow formation of cis-PtCl₂(LNa/K)₂. K₂PdCl₄ reacts more rapidly to give PdCl₂(LNa/K)₂. In homogeneous alkaline solution rapid oxidation of the phosphine occurs with only small amounts of platinum complex being observable. The biphasic reaction yields phosphine oxide in the aqueous layer and a small amount of the chelate complexes PtL₂ in the organic. Representative complexes have been isolated and characterised and the mechanisms for the reactions discussed. The electrospray mass spectra of solutions of the isolated complexes have been recorded in both positive and negative ionisation modes. The positive ionisation spectra are complicated, but platinum and palladium containing ions derived from loss of chloride, H⁺ and HCl are observed in the negative ionisation spectra.     

Structure, physical, chemical and photophysical properties of Pt(bph) (CO)2, where bph is the biphenyl dianion

The complex Pt(bph) (CO)₂ crystallizes in the space group Cmcm with a = 18.647(6), B = 9.566(2) and C = 6.4060(5) Å. The geometry of the molecule is slightly distorted from square planar with a Pt---C(CO) bond distance of 1.98(2) Å and a Pt---C(bph) bond distance of 2.04(2) Å. The Pt(bph)(CO)₂ complex serves as a precursor for the preparation of a wide variety of Pt(bph)X₂ complexes, where X = monodentate ligands such as acetonitrile, pyridine, etc., and X₂ = bidentate ligands such as bypyridine, 1,10-phenanthroline, etc. In the solid state, the complex exhibits a green color, but when ground with an alkali metal salt turns deep blue to purple. In CH₂Cl₂, the color disappears but optical transitions are observed at 271 nm (2.7 × 10⁴ M⁻¹ cm⁻¹), 303 nm (1.1 × 10⁴ M⁻¹ cm⁻¹) and 330 nm (5.5 × 10³ M⁻¹ cm⁻¹). The complex is a weak emitter exhibiting a structured spectrum in CH₂Cl₂ at r.t. with maxima located at 562 and 594 nm and an emission lifetime of 3.1 μs when excited at 337 nm.     

Hydride complexes of platinum(II) containing unsymmetrical di(phosphine) ligands: synthesis, characterization and evidence for pairwise addition of hydrogen based on parahydrogen induced polarization

Unsymmetrical di(phosphine) ligands (dpp)₂Rop (1a, b = bis(diphenylphosphino)-2-alkyl-3-oxapropane (alkyl = methyl and ethyl)) and (dpp)₂oCy (1c = trans-2-diphenylphosphinocyclohexyl diphenylphosphinite) and their Pt(II) dichloride complexes, PtCl₂((dpp)₂mop) (2a), PtCl₂((dpp)₂eop) (2b) and PtCl₂((dpp)₂oCy) (2c), have been synthesized and characterized by NMR spectroscopy. The crystal structures of 2b and 2c show that the geometry about the platinum centers is square planar. In 2b, the metal and di(phosphine) ligand chelate ring are in a chair conformation, whereas in 2c, the chelate ring conformation is a skewed boat. Initial reaction of sodium borohydride with 2a, b, c yields the monohydride monochloride complexes PtHCl((dpp)₂mop) (5a), PtHCl((dpp)₂eop) (5b) and PtHCl((dpp)₂oCy) (5c). At longer reaction times, fluxional dimeric species are obtained, [PtH((dpp)₂mop)]₂ (4a), [PtH((dpp)₂eop)]₂ (4b) and [PtH((dpp)₂oCy)]₂ (4c),and in the case of 4c two different isomers exist. The dihydride complexes PtH₂((dpp)₂mop) (3a), PtH₂((dpp)₂eop) (3b) and PtH₂((dpp)₂oCy) (3c), are prepared by further reaction of NaBH₄ and 2. Hydrogen cycling is facile in the dihydride complexes 3a, b, c, and oxidative addition of H₂ proceeds in a pairwise manner as determined by the observation of parahydrogen induced polarization (PHIP) in the ¹H NMR spectra. The reductive elimination of H₂ is also shown to be concerted by reaction of dihydride complexes with D₂. Crystal data: 2b (C₃₀H₃₂Cl₆OP₂Pt), monoclinic, space group P2₁/c (No. 14), a = 13.7040(1), b = 11.3430(7), c = 21.3880(9) Å, β = 97.923(9)°, V = 3292.9(2) ų and Z = 4; 2c (C₃₀H₃₀Cl₂OP₂Pt), monoclinic, space group P2₁ (No. 4), a = 11.7360(2), b = 8.4311(2), c = 14.2789(2) Å, β = 101.290(1)°, V = 1385.52(4) ų and Z = 2.     

Synthesis,characterization, DNA interaction,and cytotoxicity of novel Pd(II) and Pt(II) complexes

Four complexes [Pd(L)(bipy)Cl]·4H₂O (1), [Pd(L)(phen)Cl]·4H₂O (2), [Pt(L)(bipy)Cl]·4H₂O (3), and [Pt(L)(phen)Cl]·4H₂O (4), where L = quinolinic acid, bipy = 2,2’-bipyridyl, and phen = 1,10-phenanthroline, have been synthesized and characterized using IR, ¹H NMR, elemental analysis, and single-crystal X-ray diffractometry. The binding of the complexes to FS-DNA was investigated by electronic absorption titration and fluorescence spectroscopy. The results indicate that the complexes bind to FS-DNA in an intercalative mode and the intrinsic binding constants K of the title complexes with FS-DNA are about 3.5?×?10⁴ M^?1, 3.9?×?10⁴ M^?1, 6.1?×?10⁴ M^?1, and 1.4?×?10⁵ M^?1, respectively. Also, the four complexes bind to DNA with different binding affinities, in descending order: complex 4, complex 3, complex 2, complex 1. Gel electrophoresis assay demonstrated the ability of the Pt(II) complexes to cleave pBR322 plasmid DNA.     

Synthesis, platinum(II) complexes and structural aspects of the new tetradentate phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane

Several novel dimers of the composition [M₂Cl₄(trans-dppen)₂] (M=Ni (1), Pd (2), Pt (3)) containing trans-1,2-bis(diphenylphosphino)ethene (trans-dppen) have been prepared and characterized by X-ray diffraction methods, NMR spectroscopy (¹⁹⁵Pt{¹H}, ³¹P{¹H}), elemental analyses, and melting points. The intramolecular [2+2] photocycloaddition of the two diphosphine-bridges in 3 produces [Pt₂Cl₄(dppcb)] (4), where dppcb is the new tetradentate phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane. Neither 1 nor the free diphosphine trans-dppen shows this reaction. In the case of 2 the photocycloaddition is slower than in 3. This difference can be explained by the shorter distance between the two aliphatic double bonds in 3 than in 2, but also different transition probabilities within ground and excited states of the used metals could be involved. Furthermore, variable-temperature ³¹P{¹H} NMR spectroscopy of 2 or 3 reveals a negative activation entropy of 2 for the [2+2] photocycloaddition, but a positive of 3. The removal of chloride from 4 by precipitating AgCl with AgBF₄, and subsequent treatment with 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) leads to [Pt₂(dppcb)(bipy)₂](BF₄)₄ (5) and [Pt₂(dppcb)(phen)₂](BF₄)₄ (6), respectively. In an analogous reaction of 4 with PMe₂Ph or PMePh₂, [Pt₂(dppcb)(PMe₂Ph)₄](BF₄)₄ (7) and [Pt₂(dppcb)(PMePh₂)₄](BF₄)₄ (8) are formed. Complexes 1–8 show square–planar coordinations, where the compounds 4–8 have also been characterized by the above mentioned methods together with fast atom bombardment mass spectrometry (7, 8). The crystal structure of 4 reveals two conformations, which arise from an energetic competition between the sterical demands of dppcb and an ideal square–planar environment of Pt(II). The free tetraphosphine dppcb can be obtained easily from 4 by treatment with NaCN. It has been characterized fully by the above methods including ¹³C{¹H} and ¹H NMR spectroscopy. The X-ray structure analysis shows the pure MMMP-enantiomer in the solid crystal, which is therefore optically active. This chirality is induced by a conformation of dppcb, where all four PPh₂ groups are non-equivalent. Variable-temperature ³¹P{¹H} NMR spectroscopy of dppcb confirms this explanation, since the single signal at room temperature is split into two doublets at 183 K. The goal of this article is to demonstrate the facile production of a new tetradentate phosphine from a diphosphine precursor via Pt(II) used as a template.