Synthesis, solid state structure and spectro-electrochemistry of ferrocene-ethynyl phosphine and phosphine oxide transition metal complexes

The synthesis of ferrocene-ethynyl phosphine platinum dichloride complexes based on (FcCtriple bond; length of mdashC)nPh3−nP (1a, n = 1; 1b, n = 2; 1c, n = 3; Fc = ferrocenyl, (η5-C5H5)(η5-C5H4)Fe) is described. Air-oxidation of 1c afforded (FcCtriple bond; length of mdashC)3Pdouble bond; length as m-dashO (6). Treatment of 1a–1c with [(PhCtriple bond; length of mdashN)2PtCl2] (2) or [(tht)AuCl] (tht = tetrahydrothiophene) (7), respectively, gave the heterometallic transition complexes cis-[((FcCtriple bond; length of mdashC)nPh3−nP)2PtCl2] (3a, n = 1; 3b, n = 2; 3c, n = 3) or [((FcCtriple bond; length of mdashC)nPPh3−n)AuCl] (8a, n = 1; 8b, n = 2). Further treatment of these molecules with HCtriple bond; length of mdashCMc (4a, Mc = Fc; 4b, Mc = Rc = (η5-C5H5)(η5-C5H4)Ru) in the presence of [CuI] produced trans-[((FcCtriple bond; length of mdashC)Ph2P)2Pt(Ctriple bond; length of mdashCFc)2] (5) (reaction of 3a with 4a) and [(FcCtriple bond; length of mdashC)nPh3−nPAuCtriple bond; length of mdashCMc] (n = 1: 9a, Mc = Fc; 9b, Mc = Rc; n = 2: 11a, Mc = Fc; 11b, Mc = Rc) (reaction of 4a, 4b with 8a, 8b), respectively. The structures of 3a, 5, 6, 8, 9a, and 9b in the solid state were established by single-crystal X-ray structure analysis. The main characteristic features of these molecules are the linear phosphorus–gold–acetylide arrangements, the tetra-coordination at phosphorus and the square-planar surrounding at platinum. The electrochemical and spectro-electrochemical behavior of complexes 5, 8a, 9a, 9b and [(Ph3P)AuCtriple bond; length of mdashCFc] was investigated in the UV/Vis/NIR. Near IR bands that are likely associated with charge transfer from the ((FcCtriple bond; length of mdashC)Ph2P)2Pt or the ((FcCtriple bond; length of mdashC)nPh3−nP)Au (n = 0, 1) moieties appear upon oxidation of the σ-bonded ferrocene-ethynyl groups. These bands undergo a (stepwise) blue shift as ferrocene-ethynyl substituents on the phosphine coligands are oxidized.