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 <- (NN)-N-boolean AND -> M-NCN-4-SC(O)Me](OTf)(2) (Me(O)CS-4-NCN = [C6H2(CH2NMe2)(2)-2,6-SC(O)Me-4](-); (NN)-N-boolean AND = 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 (BuLi)-Bu-t, S-8 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 [Pd-2(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 (BuLi)-Bu-t, 1/8 S-8 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 d(8)-metal pincer chemistry. (C) 2008 Elsevier B.V. All rights reserved.