Peter P. Gaspar

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Name: Gaspar, Peter

Organization: Washington University , USA

Department: Department of Chemistry

Title: Professor(PhD)

TOPICS

Organic Chemistry

Chemicals
References

Theoretical Calculations on the Tetramethyldisilene Rearrangement: A New Approach to an Old Mechanistic Problem

Co-reporter:Mrinmoy Nag Dr. ;PeterP. Gaspar

Chemistry - A European Journal 2009 Volume 15( Issue 34) pp:8526-8532

Publication Date(Web):

DOI:10.1002/chem.200901024

Abstract

Roark and Peddle first observed that, when not trapped, Me₂SiSiMe₂ underwent a series of rearrangements to give two major isomeric products: 1,1-dimethyl-1,3-disilacyclobutane and 1,3-dimethyl-1,3-disilacyclobutane. The widely accepted mechanism for this rearrangement was proposed by Barton and co-workers. However, little is known about the thermodynamic or kinetic properties of this reaction, because the relevant data are limited to the product ratios of the two isomers. Our calculations predict that the product ratio is driven by kinetic control rather than thermodynamic control. We also show that new DFT functionals, such as MPW1K and M052X, produce thermochemical results comparable with CCSD(T) calculations.

Synthesis of 1-Stannacyclopent-3-enes and Their Pyrolysis to Stannylenes

Co-reporter:Dong Zhou, Clemens Reiche, Mrinmoy Nag, John A. Soderquist and Peter P. Gaspar

Organometallics 2009 Volume 28(Issue 8) pp:2595-2608

Publication Date(Web):March 31, 2009

DOI:10.1021/om800541f

1,1-Diorgano-1-stannacyclopent-3-enes have been synthesized by condensation in THF of magnesium complexes of 1,3-dienes and dichlorodiorganostannanes. 1,1-Dimethyl-, 1,1-di-n-butyl-, 1,1-di-tert-butyl-, and 1,1-diphenyl-1-stannacyclopent-3-enes and 1,1,3,4-tetramethyl-, 1,1-di-tert-butyl-3,4-dimethyl-, and 3,4-dimethyl-1,1-diphenyl-1-stannacyclopent-3-enes were prepared. Kinetic studies of the pyrolysis at temperatures as low as 75 °C of several of these stannacyclopent-3-enes resulted in their first-order disappearance, consistent with a unimolecular dissociation to the corresponding stannylene and diene. Activation parameters are reported. Trapping of dimethylstannylene by dienes was overwhelmed by oligomerization of Me2Sn:, but for t-Bu2Sn: a high yield of diene adduct was obtained. The dimethylstannylene oligomer(s) functioned as stannylenoids and were responsible for several reactions previously attributed to free Me2Sn:. cyclo-(t-Bu2Sn)4 may also function as a stannylenoid.

A Computational Study of the Mechanism of Addition of Singlet Carbene Analogues to 1,3-Butadiene to Form 1,1-Dimethylmetallacyclopent-3-enes [MMe2C4H6, M = Si, Ge, Sn] and Their Reverse Retro-addition Reactions

Co-reporter:Mrinmoy Nag and Peter P. Gaspar

Organometallics 2009 Volume 28(Issue 19) pp:5612-5622

Publication Date(Web):September 10, 2009

DOI:10.1021/om900369e

B3LYP, MPW1K, and CCSD(T) electronic structure calculations were employed to investigate the mechanisms for the addition of singlet carbene analogues dimethylsilylene, Me2Si:, dimethylgermylene, Me2Ge:, and dimethylstannylene, Me2Sn:, to 1,3-butadiene to form 1,1-dimethylmetallacyclopent-3-enes and their reverse retro-addition reactions. The calculations suggest that silylenes and germylenes add to 1,3-butadiene to form the 1,2-adduct, vinylmetalliranes, and the 1,4-adduct, metallacyclopent-3-enes, via 1,2-addition and concerted 1,4-addition processes, respectively, while stannylenes add exclusively to form the 1,4-adduct. Our calculations also predict that direct rearrangements of vinylmetalliranes make minimal contribution to the formation of the 1,4-adducts since the retro-addition reactions of the metallylenes followed by 1,4-addition are much faster than the rearrangement reactions of vinylmetalliranes to form metallacyclopent-3-enes.