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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 8, Number 3
March 20, 1987 

Synthesis and Dissociation Constants of Cationic Rhodium (Ⅰ)-Triphenylarsine Complexes of Unsaturated Nitriles and Aldehyde
Chong Shik Chin*, Jeonghan Park, Sang Young Shin, Choongil Kim
Reactions of Rh(ClO4)(CO)(AsPh3)2 with unsaturated nitriles and aldehyde, L, produce a series of new cationic rhodium (Ⅰ) complexes, [RhL(CO)(AsPh3)2]ClO4 (L = CH2 = CHCN, CH2 = C(CH3)CN, trans-CH3CH = CHCN, CH2 = CHCH2CN, trans-C6H5CH = CHCN, and trans-C6H5CH = CHCHD) where L are coordinated through the nitrogen and oxygen, respectively but not through the π-system of the olefinic group. Dissociation constants for the reaction, [RhL(CO)(AsPh3)2]ClO4 ↔ Rh(ClO4)(CO)(AsPh3)2 + L, have been measured to be 1.20 × 10-4 M (L = CH2 = CHCN), 1.05 × 10-4 M (L = CH2 = C(CH3)CN, 3.26 × 10-5 M (L = trans-CH3CH = CHCN) and 6.45 × 10-5 M (L = CH2 = CHCH2CN) in chlorobenzene at 25℃, and higher than those of triphenylphosphine complexes, [RhL(CO)(PPh3)2]ClO4 where L are the corresponding nitriles that are coordinated through the nitrogen atom. The differences in dissociation constants seem to be predominantly due to the differences in ΔH (not due to the differences in ΔS). The weaker Rh-N (unsaturated nitriles) bonding in AsPh3 complexes than in PPh3 complexes (based on ΔH values) suggests that the unsaturated nitriles in 2∼5 are good σ-donor and poor π-acceptor.
179 - 183
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