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

Abstract

The alkynylation of [Cp*MX2(PEt3)] (Cp* = η5-C5Me5; X = Cl, M = Rh; X = I, M = Ir) with an excess of LiC⋮CR (R = Ph (a), tBu (b), SiMe3 (c)) in thf leads to novel bis(alkynyl) [Cp*M(C⋮CR)2(PEt3)] (M = Rh, 3a−c; M = Ir, 4a,c) or mono(alkynyl) [Cp*M(C⋮CR)X(PEt3)] (M = Rh, X = Cl, 1a−c; M = Ir, X = I, 2c‘) complexes depending on the reaction time. 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 [Cp*IrX2(PEt3)] with [AgC⋮CPh]n. Complexes 1−4 undergo facile reaction with [cis-M‘(C6F5)2(thf)2] (M‘ = Pt, Pd; thf = tetrahydrofuran), affording homobridged bis(μ-alkynyl) [(PEt3)Cp*M(μ-C⋮CR)2M‘(C6F5)2] (M = Rh, M‘ = Pt (5a,c), Pd (6a,c); M = Ir, M‘ = Pt (7a,c), Pd (8a,c)) or heterobridged μ-alkynyl−μ-halide [(PEt3)Cp*M(μ-C⋮CR)(μ-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 compounds. Complexes 5a,c and 7a,c can, alternatively, be obtained through a neutralization reaction between the dianionic complexes Q2[cis-Pt(C6F5)2(C⋮CR)2] (R = Ph, Q = PMePh3; R SiMe3, Q = NBu4) and solvento species [Cp*M(PEt3)(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) complexes have been determined by X-ray analyses. In the iridium mixed complexes 7a,c, 8a, and 12a the alkynyl ligands are σ-bonded to iridium and π-bonded to Pt (7a,c) or Pd (8a, 12a) centers. In contrast, the crystal structure of 5c shows a dinuclear zwitterionic complex formed by two different alkynyl organometallic termini, [Cp*Rh+(C⋮CSiMe3)(PEt3)] and [cis-Pt-(C6F5)2(C⋮CSiMe3)], held together through η2-bonding of the alkynyl groups.