Carbon−Carbon Bond Formation Promoted by Adjacent Metal Centers: Regioselective Alkyne Insertions into a “Rh(μ-CH2)Ru” Moiety Yielding C3- and C5-Bridged Fragments

Abstract

The heterobinuclear complex [RhRu(CO)3(μ-CH2)(dppm)2][CF3SO3] (2) (dppm = Ph2PCH2PPh2), generated in situ from the tetracarbonyl precursor, reacts with the alkynes, dimethyl acetylenedicarboxylate, hexafluoro-2-butyne, and diethyl acetylenedicarboxylate to give the C3-bridged products [RhRu(CO)3(μ-η1:η1-C(R)C(R)CH2)(dppm)2][CF3SO3] (R = CO2CH3 (3), CF3 (4), CO2CH2CH3 (5)), in which the alkynes have inserted into the Rh−C bond of the bridging methylene group. Compound 2 also reacts with 2-butyn-1-al diethylacetal and 2-butyn-1-ol, producing the insertion products [RhRu(CO)3(μ-η1:η1-C(CH3)C(R)CH2)(dppm)2][CF3SO3] (R = CH(OEt)2 (6), CH2OH (7)) analogous to compounds 3−5. The regiochemistry of alkyne insertion in both cases has been established by 2-D NMR spectroscopy; the methyl substituent is adjacent to Rh, and the oxygen-containing substituent is adjacent to the methylene group. Attempts to generate an isomer of 3 by the reverse sequence of methylene insertion into the Rh−C bond of the alkyne-bridged species [RhRu(CO)3(μ-η1:η1-C(CO2CH3)C(CO2CH3))(dppm)2][X] (X = BF4 (8a), CF3SO3 (8b)) failed with no reaction occurring, although reaction of the dicarbonyl analogue, [RhRu(OSO2CF3)(CO)2(μ-η1:η1-C(CO2CH3)C(CO2CH3))(dppm)2], with CH2N2 results in methylene insertion into the Rh−Ru bond to give [RhRu(OSO2CF3)(CO)2(μ-CH2)(μ-η1:η1-C(CO2CH3)C(CO2CH3))(dppm)2] (10). Reaction of 3 with trimethylamine-N-oxide results in loss of a carbonyl and a rearrangement of the C3-bridged group, affording [RhRu(CO)2(μ-η1:η3-CHC(CO2CH3)CH(CO2CH3))(dppm)2][CF3SO3] (11). Propargyl alcohol reacts with 2, affording a double-insertion product [RhRu(CO)2(μ-η2:η4-CHC(CH2OH)CHC(CH2OH)CH2)(dppm)2][CF3SO3] (12) with incorporation of two propargyl alcohol units in a head-to-tail arrangement. The structures of compounds 4, 8a, and 12 were determined by X-ray methods.