Ultrafast Infrared Studies of the Reaction Mechanism of Silicon−Hydrogen Bond Activation by η⁵-CpV(CO)₄

Abstract

The photochemical Si−H bond activation reaction by the group VB, d4 organometallic compound η 5 -CpV(CO)4 (Cp = C5H5) has been studied in neat triethylsilane under ambient conditions. The spectral evolutions of the metal-bonded CO stretching bands were monitored from 300 fs to 800 ps following UV photolysis using femtosecond pump−probe spectroscopic methods. The reactive intermediates observed on the ultrafast time scale were also studied using density functional theory as well as ab initio quantum chemical modeling. It was found that photolysis of vanadium tetracarbonyl resulted in the formation of tricarbonyls in either the singlet or triplet electronic state following CO loss. The subsequent reaction was partitioned into two pathways by the initial solvation of the tricarbonyls through the Si−H bond or an ethyl group of the solvent molecule. Knowledge of the elementary reaction steps including changes in molecular morphology and electronic multiplicity allowed a comprehensive description of the chemical reactivity.

Reactions of Hydrosilanes with Transition Metal Complexes and Characterization of the Products

“…The photochemically induced loss of CO from η 5 -CpM(CO) 3 (M ) Mn, Re), 165a η 5 -CpV(CO) 4 , 141 and M(CO) 6 (M ) Cr, Mo, W), 83 in neat Et 3 SiH under ambient conditions, has been studied with femtosecond pump-probe spectroscopic methods. The studies of the Mn and Re systems have been summarized by Harris and co-workers in an Accounts of Chemical Research article.…”

“…141 Both singlet and triplet CpV(CO) 3 species were formed with different geometries for the two different electronic states (eq 43). The data suggested that the triplet species reacted rapidly through a concerted spin crossover/solvation facilitated by the SiH bond of Et 3 SiH (producing 3-11a).…”

Organometallic photochemistry at the end of its first century

“…Triplet species such as CpV(CO) 3 , CpCo(CO), and Fe(CO) 4 do not form agostic bonds with hydrocarbons and thus tend to react with Si-H bonds to directly form oxidative addition products [59,60]. Perhaps counter intuitively, singlet intermediates such as CpRh(CO) and CpRe(CO) 2 on the average take longer Scheme 6. to form oxidative addition products since they are prone to form modestly stable agostic species with the hydrocarbon moieties in silanes, thus Si-H activation must await rearrangement of these intermediates [61].…”

Investigation of organometallic reaction mechanisms with one and two dimensional vibrational spectroscopy

“…Pump-probe spectroscopy has been extensively used to understand these types of dynamics [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], and this work applies the same pump-probe methodologies as well as a relatively new technique, two dimensional infrared spectroscopy, to the photophysics and reactions of several prototypical organometallic complexes [20][21][22][23][24][25][26].…”