Formation of [Cr(CO)_<i>x</i>(Ph₂PN(<i>i</i>Pr)PPh₂)]⁺ Structural Isomers by Reaction of Triethylaluminum with a Chromium <i>N,N</i>-Bis(diarylphosphino)amine Complex [Cr(CO)₄(Ph₂PN(<i>i</i>Pr)PPh₂)]⁺: An EPR and DFT Investigation

Abstract

The interaction of triethylaluminum (TEA) with a solution of the paramagnetic Cr(I) bis(phosphine) complex [Cr(CO) 4 1 ][Al(OC(CF 3 ) 3 ) 4 ] ( 1 = Ph 2 PN( i Pr)PPh 2 ) has been studied using EPR and DFT. It was found that the TEA is responsible for the complete removal of all CO groups from the [Cr(CO) 4 1 ] + complex, producing the [Cr( 1 -bis-η 6 -arene)] +, and this reaction occurs via a dominant pathway involving a series of [Cr(CO) x 1 ] + ( x < 4) intermediates, consistently including the cis -[Cr(CO) 3 1 ] + complex (species A) and the “piano-stool”-type [Cr(CO) 2 1 ] + complex (species C). A further [Cr(CO) 2 1 ] + intermediate complex (labeled species D, which is a structural isomer of species C) was also identified experimentally, suggesting a second pathway for TEA activation may also be operative. All of these paramagnetic complexes have been characterized by CW EPR, and the spin Hamiltonian parameters were verified using DFT. The distribution and type of [Cr(CO) x 1 ] + intermediates formed were found to be very sensitive to the experimental conditions, including the quantity and manner of TEA addition, the temperature of activation, and the aging time of the solution.