~) Pergamon S0277-5387(96) 00020-4 Pol!hedron Vol. 15, No. 18, pp. 3093 3100, 1996 Copyright ,3~, 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0277 5387/96 $15.00+0.00 THE MECHANISM OF THE PHOTOREACTION OF cis-Ols-CsMes)Re(CO)212 WITH P(OMe)3 WENJIA XIA and ROSS H. HILL* Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6 and A. HUGO KLAHN,* CARMEN LEIVA and G. E. BUONO-CORE Instituto de Quimica, Universidad Cat61ica de Valparaiso, Casilla 4059, Valparaiso, Chile (Received 18 September 1995; accepted 13 December 1995) Abstract Photolysis of cis-(~/5-CsMes)Re(CO)212 in the presence of P(OMe)3 led to the production of [(q5-CsMes)Re(CO)2P(OMe)3], MeI and OP(OMe)2I. The mechanism of the reaction has been studied both by low temperature and room temperature FTIR spec- troscopy and by measurement of the quantum yields under conditions of varying P(OMe)3 concentration. The reaction occurs via initial loss of I- to generate the solvent caged ion pair [(r/5-C5Mes)Re(CO)2I]+I . This species then reacts with P(OMe)3 either within the solvent cage or following escape from the solvent cage, to form [(r/5-C5Mes)Re (CO)2(THF)I] +. This complex then reacts with P(OMe)3 to generate the final products, [(r/5-CsMes)Re(CO)2P(OMe)3], MeI and P(O)I(OMe)2. Copyright © 1996 Elsevier Science Ltd Recently, the synthesis of [(qS-CsMes) Re (CO)2P(OMe)3] has been reported from our lab- oratory. 1 In this work, we have demonstrated that the compound can be synthesized by photolysis of (qS-CsMes)Re(CO)3 in the presence of P(OMe)3. This product can also be formed by the reaction of Cp*Re(CO)212 with excess of P(OMe)3 in boiling toluene. 2 More recently, we have found that photo- lysis of 015-CsMe5)Re(CO)212 in the presence of excess P(OMe)3 provides an alternative route to [(qs-CsMes)Re(CO)2P(OMe)3]. This in itself was not surprising; however, it was not obvious how this reaction occurred given the earlier study on the mechanism of the cis-trans isomerism of (r/5- CsMes)Re(CO)2X2 (X = Me, CI, Br, I) at 12 K. In this study, 3 it was found that the isomerism occurred via initial CO loss to produce a common * Authors to whom correspondence should be addressed. 16-electron intermediate, (qS-CsMes)Re(CO)X2, from both the cis and trans isomers. This fragment reacted with the photogenerated CO, trapped in the low temperature glass, to yield only the trans isomer upon warming to 100 K. In a later study on the photochemistry of (qs-CsMe5)Re(CO)2Br2 on a sili- con surface, at 77 K, a second isomer of the unsatu- rated species was identified, which upon reaction with CO generated the cis isomer? If the CO loss mechanism described above also operated at room temperature, the product of reac- tion of (r/5-CsMes)Re(CO)212 with P(OMe)3 would be expected to be [(r/5-CsMes)Re(CO)P(OMe)312] (which has recently been prepared as the cis isomer by Me3NO-induced decarbonylation of the cation [Cp*Re(CO)2P(OMe)3I] +).5 This product was not observed, nor was [(r/5-CsMes) Re (CO)(THF)P(OMe)3] [if the reaction was carried out in tetrahydrofuran (THF) solution], which could be formed following I2 loss from the initially formed monophosphite complex. The only 3093