SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF NEW ALKYNYL COMPLEXES OF RHODIUM AND IRIDIUM - PREPARATION OF NEUTRAL (M-M' M = RH, IR, M' =PT, PD) HETERO-ALKYNYL-BRIDGED DINUCLEAR COMPLEXES

The alkynylation of [CpMX2(PEt3)] (Cp* = eta(5)-C5Me5; X = Cl, M = Rh ; X = I, M = Ir) with an excess of LiC=CR (R = Ph (a), Bu-t (b), SiMe3 (c)) in thf leads to novel bis(alkynyl) [CpM(C=CR)(2)(PEt3)] (M = Rh , 3a-c; M = Ir, 4a,c) or mono(alkynyl) [CpM(C=CR)X(PEt3)] (M = Rh, X = Cl, 1a-c; M = Ir, X = I, 2c') complexes depending on the reaction ti me. Complex 4a and the related (phenylethynyl)iridium derivatives [Cp Ir(C=CPh)X(PEt3)] (X = Cl, 2a; X = I, 2a') can be prepared by reacting [CpIrX2(PEt3)] with [AgC=CPh](n). Complexes 1-4 undergo facile react ion with [cis-M'(C6F5)(2)(thf)(2)] (M' = Pt, Pd; thf = tetrahydrofuran ), affording homobridged bis(mu-alkynyl) [(PEt3)CpM(mu-C=CR)(2)M'(C6F 5)(2)] (M = Ph, M' = Pt (5a,c), Pd (6a,c); M = Ir, M' = Pt (7a,c), Pd (8a,c)) or heterobridged mu-alkynyl-mu-halide [(PEt3)CpM(mu-C=CR)(mu- X)M'(C6F5)(2)] (M = Rh, X = Cl, M' = Pt (9a-c), Pd (10a,b); M = Ir, X = Cl, I, M' = Pt (11a,a',c'), Pd (12a,a',c')) heterodinuclear compound s. Complexes 5a,c and 7a,c can, alternatively, be obtained through a n eutralization reaction between the dianionic complexes Q(2)[cis-Pt(C6F 5)(2)(C=CR)(2)] (R = Ph, Q = PMePh3; R =SiMe3, Q = NBu4) and solvento species [CpM(PE(t)3)(acetone)(2)](ClO4)(2) (M = Rh, Ir) (prepared in situ). The molecular structures of the heterobridged Rh-Pt (9b) and Ir -Pd (12a) and homobridged Rh-Pt (5c), Ir-Pt (7a,c), and Ir-Pd (8a) com plexes have been determined by X-ray analyses. In the iridium mixed co mplexes 7a,c, 8a, and 12a the alkynyl ligands are a-bonded to iridium and,pi-bonded to Pt (7a,c) or Pd (8a, 12a) centers. In contrast, the c rystal structure of 5c shows a dinuclear zwitterionic complex formed b y two different alkynyl organometallic termini, [CpRh+(C=CSiMe3)(PE(t )3)] and [cis-Pt-(C6F5)(2)(C=CSiMe3)], held together through eta(2)-bo nding of the alkynyl groups.