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.

Resumen

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′(C 6F5)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′(C 6F5)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≡CSiMe 3)], held together through η2-bonding of the alkynyl groups.