Structural Characterization of (C₅H₅)Co(PPh₃)(η²-alkyne) and (C₅H₅)Co(η²-alkyne) Complexes of Highly Polarized Alkynes

Abstract

The solid state structures of the cobalt−alkyne complexes (η 5 -C 5 H 5 )(PPh 3 )Co{η 2 -(R 3 Si)CC(SO 2 Ar)} (3-TMS, R = Me, Ar = C 6 H 5 ; 3-TIPS, R = CH(CH 3 ) 2 , Ar = p-C 6 H 4 CH 3 ) and the noncoordinated alkyne (Me 3 Si)CC(SO 2 Ph) (6-TMS) have been characterized by X-ray crystallography and, in the case of 3-TMS, 6-TMS, and (η 5 -C 5 H 5 )Co{η 2 -(Me 3 Si)CC(SO 2 Ph)} (5-TMS-calc), by B97D/Def2-TZVPP computational analysis. The phosphine-dissociated complex 5-TMS-calc is determined to be a ground state singlet. Analysis of bond angle and distance metrics, calculated NMR chemical shift data, and molecular orbital analysis provide strong evidence for a four-electron-donor alkyne ligand in 5-TMS-calc. The degree of asymmetry in metal−alkyne bonding, as defined by the Gladysz alkyne-slippage parameter, is dramatically reduced in 5-TMS-calc relative to that in the precursor complex 3-TMS-calc.

Enol Ester Synthesis via Cobalt-Catalyzed Regio- and Stereoselective Addition of Carboxylic Acids to Alkynes

“…20c CpCo/alkyne complexes can also be synthesized from Co(I) and alkynes. 21 A stoichiometric reaction of CoCl•L5 and benzoic acid was conducted to check the possibility of path a. However, none of the new species was observed by 1 H NMR spectroscopy (see the SI).…”

“…A similar mechanism was proposed and calculated by the Breit group in the catalytic reaction by rhodium, in which the barrier for intramolecular protonation was lower than that in path a . CpCo/alkyne complexes can also be synthesized from Co­(I) and alkynes . A stoichiometric reaction of CoCl· L5 and benzoic acid was conducted to check the possibility of path a.…”

Side-On Coordination of Nitrous Oxide to a Mononuclear Cobalt Center

“…The preference for η 2 - N,N coordination in 2 can be rationalized on the basis of the electronic characteristics of both the cobalt coordination environment in 2 and the π* system of N 2 O. The Cp*Co­(CNAr Tripp ) fragment is a derivative of the generic CpCo­(L) coordination platform (L = CO, PR 3 ), which has been used extensively for π-coordination of olefins, alkynes, and other unsaturated substrates. − This utility of CpCo­(L) is derived from the strong π-basic character of the d 8 cobalt center in the plane parallel to the cyclopentadienyl ring. Whereas the π* system of N 2 O possesses greater nitrogen than oxygen character, η 2 - N,N coordination additionally allows for the accumulation of electron density on the more electronegative oxygen atom (Scheme ).…”

Mechanism and Stereoselectivity of the Elementometalation Process of Activated Alkyne RCCR(RCO2Me) by Cp2TaH3

“…Recently, the synthesis and characterization of metal alkyne complexes have been reported by some groups . The reactivity, stereochemistry, and mechanism of alkyne or alkene insertion into ME bonds have also received increasingly more attention.…”