I. Time resolved spectroscopic studies of reactive intermediates in cobalt and rhodium catalyzed alkene and alcohol carbonylations. II. Photochemistry of dichlorocarbonyl(nitrosyl hydride)bis(triphenylphosphine)osmium(II): Photochemical production of nitrosyl hydride in solution.

摘要

I. The photochemistry of Co₂(CO)₆(PMePh2) ₂ (A) was examined using a combination of UV-Visible, FTIR, and time-resolved infrared (TRIR) techniques. Species generated by photolysis of A may be relevant to the catalytic hydroformylation of olefins. Two primary products were formed upon photolysis of A: Co(CO)₃(PMePh ₂) and Co₂(CO)₅(PMePh₂)₂. The reactivity of each of these species was investigated using flash photolysis with TRIR detection.; Co₂(CO)₅(PMePh₂)₂ reacts with CO to re-form A with a rate constant of ∼4 × 10 6 M−1 s−1. Its reaction with PMePh₂ to form Co₂(CO)₅(PMePh₂ )₃ is about an order of magnitude faster.; Co(CO)₃PMePh₂, a seventeen electron metal radical, reacts in a number of ways. Two units of Co(CO)₃(PMePh₂) readily recombine to form A. Co(CO)₃(PMePh₂) extracts a chloride atom from 1,2-dichloroethane to form Co(CO)₃(PMePh ₂)Cl. It also undergoes rapid substitution, reacting with CO to form Co(CO)₄ and with PMePh₂ to form Co(CO)₂(PMePh ₂)₂.; The thermal and photochemical reactivity of Rh(C(O)CH₃)(CO) ₂I₃− (B) were also investigated. B is an intermediate in the industrially important catalytic carbonylation of methanol. B reductively eliminates CH₃C(O)I to form Rh(CO)₂I₂−, and the rate of this reaction was studied as a function of [CO]. Photolysis of B accelerates reductive elimination. TRIR studies were consistent with a mechanism in which reductive elimination occurred through a five-coordinate intermediate formed by CO loss. A mechanism was proposed that relates the observed photochemical reactivity to the thermal reactivity.; II. HNO has recently been proposed as a biologically important molecule, but it is difficult to study directly because of its thermal instability. Continuous wave photolysis and TRIR studies of Os(N(O)H)(CO)Cl₂(PPh₃)₂ (C) were carried out to investigate its utility as a photochemical HNO deliverer. Formation of N₂O upon photolysis of C indicated that HNO was indeed photochemically liberated. In addition, a proposed Os-linear nitrosyl species was formed, possibly through dissociation of CO. A mechanism involving two initial photoproducts is proposed to account for the observed net photochemistry.