Ligand intermediates in metal-catalyzed reactions. Annual technical report, September 1, 1990--August 31, 1991

Abstract

September6, 1991 I. RESEARCHPROGRESS This has been an extremelyproductiveprojectperiod. Six new papers have appeared in print or been acceptedfor publicationsince the previousreport (A9-14). Principalachievementsare as follows. A. 7/0 Equilibriain Aldehyde and Ketone Complexes(pub.A-8t A-11) Aldehyde and ketone complexesare intermediates in many metal-catalyzed reactions. We have sought to define the fr.ctors that affect the thermodynamics of 7/0 binding,and differencesin reactivityof the two bindingnw}des. In the pI'evious report, we describedfifteen aromaticaldehydecomplexesof the form-5_C5H 5 ula [(n)Re(NO)(PPh3)(O=CHAr)] + BF4. IR analyses (CH2Cl 2) showed these to be >96:<4 to 15:85mixturesof 7/0 isomers (vNO: _ 1745-1733;o 1701-1692 cm-1). Electronwithdrawingsubstituer0ts (whichenhance aldehyde_ acidityand lower o basicity)favor the _ bindingmode, while electrondon6ting substituents have ar oppositeeffect. We wonder._d whether parallelelectroniceffectsmight be observablein ketone complexes. Methyl ketonecomplexes [(nS-c5H5)Re(NO) (PPh3)(nI-o=C(CH3)R) ]+ X-exist exclusivelyas o isomers. Thus, we sought to prepare analogswith electron-withdrawing ketonesubstituents. Accordingly,reactionsof dichloromethane c_,plex [(n5-CsH5)Re(NO) (PPh 3)(CICH2Cl) ]+ BF4" (I) with 1,3-dichloroacetoneand 1,3-difluoroacetone gave the _ complexes[(n5,C5H5)Re(NO)(PPh3)(n 2