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The C2-, C3-, and C4-bridged bis(2,3,4,5-tetramethylphospholes) (1a, X = C2H4; 1b, X = C3H6; 1c, X = (CH2)2C6H4) and their corresponding palladium complexes [(P-P)PdCl2] (2a−c) have been prepared and characterized. A single-crystal X-ray analysis of [{bis(2,3,4,5-tetramethylphospholyl)-o-xylene}PdCl2] (2c) reveals that 1c forms a seven-membered chelate; the phosphole rings are oriented perpendicular to the PdP2Cl2 plane. Methanol solutions of [(P-P)Pd(OAc)2] (3a, P-P = 1b; 3b, P-P = 1c) and methanesulfonic acid are active for the copolymerization of ethylene and carbon monoxide, generating high-molecular-weight polymers with narrow molecular weight distributions. Under our conditions, the activity of catalyst systems containing 1c is comparable to that based on bis(diphenylphosphino)propane (dppp).

The binuclear allenyl complex [Fe2(CO)6(μ-PPh2){μ-η1:η2 α,β-(H)CαCβCγH2}] (1) has been prepared, and its reactivity with organolithium nucleophiles is described. Prop-2-yne bromide reacts with [Fe2(CO)7(μ-PPh2)]-Na+, via an SN2 mechanism, to give [Fe2(CO)6(μ-PPh2){μ-η1:η2 α,β-(H)CαCβCγH2}], the first example of a phosphido-bridged allenyl complex. The molecular structure of [Fe2(CO)6(μ-PPh2){μ-η1:η2-(H)CαCβCγH2}] (1) was determined by single-crystal X-ray diffraction and shows that the allenyl ligand is coordinated through Cα−Cβ. Variable-temperature 1H and 13C NMR studies reveal a high-energy exchange process that equilibrates the diastereotopic allenyl protons, presumably via a zwitterionic intermediate, as well as two independent trigonal rotations that act to exchange the carbonyl ligands on each unique Fe(CO)3 group. Complex 1 reacts with organolithium reagents (RLi; R = Me, nBu, Ph, C4H3S), via allenyl−carbonyl−nucleophile coupling, to afford the binuclear β,γ-unsaturated ketones [Fe2(CO)5{P(OMe)3}(μ-PPh2)(μ-η1:η2-{RC(O)CH2}CCH2)] (R = Me, 3a; nBu, 3b; Ph, 3c; C4H3S, 3d), and a single-crystal X-ray structure determination of 3a was undertaken to confirm the connectivity of the hydrocarbyl ligand. The most likely mechanism for the formation of 3a − d involves nucleophilic attack of R- at CO to give an acylate intermediate followed by migration of RCO to Cα of the allenyl and protonation of the resulting enolate to give the unstable alkenyl complexes [Fe2(CO)5(μ-PPh2)(μ-η1(C):η1(C):η2(C)-{RC(O)CH2}CCH2)] (R = Me, 2a; Bu, 2b; Ph, 2c; C4H3S, 2d). Finally, substitution of the metal-coordinated ester carbonyl in 2a − d with trimethylphosphite affords 3a − d as stable crystalline products.

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