Linear homobimetallic 4-thioacetyl-substituted NCN pincer palladium(II) and platinum(II) complexes with N-bidentate connecting units (NCN = [C 6H 2(CH 2NMe 2) 2-2,6-R-4] −)

Abstract

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 = [C 6H 2(CH 2NMe 2) 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-C 6H 2(CH 2NMe 2) 2-3,5-Br-4) ( 1) with t BuLi, 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, OSO 2CF 3) gave [Pd(NCN-4-SC(O)Me)(H 2O)][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(SEt 2)] 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)(H 2O)][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 t BuLi, 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.