Linear homobimetallic 4-thioacetyl-substituted NCN pincer palladium(II) and platinum(II) complexes with N-bidentate connecting units (NCN = [C6H2(CH2NMe2)2-2,6-R-4]?)

The synthesis and characterization of homobimetallic palladium and platinum complexes of type (Me(O)CS-4-NCN–M ← N^∩N → M–NCN-4-SC(O)Me](OTf)₂ (Me(O)CS-4-NCN = C₆H₂(CH₂NMe₂)₂-2,6-SC(O)Me-4]^?; N^∩N = 4,4′-bipyridine (bipy); M = Pd, 12; M = Pt, 13) is reported. The required bifunctional thio-acetyl NCN pincer starting compound NC(Br)N-4-SC(O)Me (2) has been synthesized by the consecutive reactions of NC(Br)N–I (I-1-C₆H₂(CH₂NMe₂)₂-3,5-Br-4) (1) with ^tBuLi, S₈ and Me(O)CCl, respectively. Chemoselective metallation at the C_aryl–Br bond was achieved by the reaction of 2 with the palladium(0) source Pd₂(dba)₃] (3) (dba = dibenzylidene acetone). Treatment of thus formed Pd(NCN-4-SC(O)Me)(Br)] (4) with AgOTf] (8) (OTf = triflate, OSO₂CF₃) gave Pd(NCN-4-SC(O)Me)(H₂O)]OTf] (9) which was further reacted with 0.5 equiv. of 4,4′-bipyridine (11a) to afford rigid-rod structured 12. When Pt(tol)₂(SEt₂)]₂ (5) (tol = 4-tolyl) was used instead of 3, then 13 was produced via the in situ formation of PtBr(NCN-4-SC(O)Me)] (7) and Pt(NCN-4-SC(O)Me)(H₂O)]OTf] (10). Another possibility to synthesize 7 relied upon the subsequent reaction of 1 with 0.5 equiv. of 5 to give PtBr(NCN-4-I)] (6) which further reacted with ^tBuLi, 1/8 S₈ and Me(O)CCl to afford 7. The cyclic voltammograms of 2, 7, and 13 are discussed.Complex 7 was structurally characterized by single crystal X-ray crystallography. Organometallic 7 crystallizes with three independent molecules in the asymmetric unit and displays a monomeric structure as commonly encountered in d⁸-metal pincer chemistry.