Synthesis, Structure, and Reactivity of Stable Alkyl and Aryl Iodide Complexes of the Formula [(η5-C5H5)Re(NO)(PPh3)(IR)]+BF4


Reaction of methyl complex (η5-C5H5)Re(NO)(PPh3)(CH3) with HBF4*Et2O (CH2Cl2, −78 °C) and then alkyl and aryl iodides RI gives adducts [(η5-C5H5)Re(NO)(PPh3)(IR)]+BF4−(3: R = a, CH3; b, CH2CH3; c, CH2CH2CH3; d, CH2CH2CH2CH3; e, CH2Si(CH3)3; f, CH2CH2CH2C1; g, CH2C1; h, C6H5; i, p-C6H4OCH3; 63-87%). The structure of 3e.(CH2Cl2)0.5 is confirmed by X-ray crystallography and compared to that of iodide complex (η5-C5H4CH3)Re(NO)(PPh3)(I) [Re-I, 2.678 (1), 2.7210 (9) Å]. The C—I bond [2.18 (1) Å] is not significantly longer than those in free alkyl iodides. Complexes 3a-c decompose (48–60 h, CD2Cl2, 25 °C) to bridging halide complexes (SS,RR)-[(η5-C5H5)Re(NO)(PPh3)]2X+BF4−[X = I (46-65%), Cl (29-48%)] and react with CH3CN to give acetonitrile complex [(η5-C5H5)Re(NO)(PPh3)(NCCH3)]+BF4~(82-87%) and RI (72-82%). Complexes 3a-c rapidly alkylate PPh3 (<15 min, CDC13) to give phosphonium salts Ph3PR+BF4−(93-86%) and iodide complex (η5-C5H5)Re(NO)(PPh3)(I) (>99-92%). The reaction of 3b and PPh3 is second order (ΔH* = 12.9 ± 0.6 kcal/mol, ΔS* = −12.0 ± 0.9 eu) and (3.3 ± 1.3) X 105 faster (298 K) than that of ICH2CH3 and PPh3 to give Ph3PCH2CH3+I−(ΔH* = 16.3 ± 0.4 kcal/mol, ΔS* = −25.9 ± 1.5 eu). Complex 3b reacts similarly with Br−, but 3h yields IC6H5 and (η5-C5H5)Re(NO)(PPh3)(Br). Ethyl bromide and chloride complexes analogous to 3b are less stable but can be prepared in situ. © 1989, American Chemical Society. All rights reserved.

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Journal of the American Chemical Society