Degree Type

Dissertation

Date of Award

1992

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

L. Keith Woo

Abstract

The preparation and characterization of carbene complexes and the first donor-stabilized silylene complexes of osmium meso-tetra-p-tolylprophyrin, Os(TTP), are described. The silylene complex (TTP)Os = SiMe[subscript]2·THF (1·THF) is prepared by the reaction of (Os(TTP)) [subscript]2 with hexamethylsilacyclopropane. Treating K[subscript]2 (Os(TTP)) with Cl[subscript]2SiR[subscript]2 also generates the silylene complexes (TTP)Os = SiR[subscript]2·THF (R = Me (1·THF), Et (2·THF), or [superscript] iPr (3·THF)). [superscript]1H NMR spectroscopy indicates that, in solution, one molecule of THF is coordinated to the silicon in these complexes. This has been verified by 2D-NOESY experiments. Addition of one equivalent of pyridine to 1·THF or 2·THF replaces the THF on silicon with pyridine, as verified by a 2D-NOESY experiment. The structure of the diethyl complex 2·THF was determined by a single-crystal X-ray diffraction experiment. This complex crystallizes with two additional THF molecules as solvates in the monoclinic space group P2[subscript]1/c with a = 21.649(5) A, b = 13.829(3) A, c = 19.526(3) A, [beta] = 98.08(2)[superscript]·, V = 5788(4) A[superscript]3, Z = 4, R = 5.0%, and R[subscript] w = 5.7%. The Os = Si distance (2.325(8) A) is the shortest observed to date;The carbene complexes, (TTP)Os = CRR[superscript]' (R = R[superscript]' = p- C[subscript]6H[subscript]4- CH[subscript]3 (5); R = H, R[superscript]' = TMS (6), Co[subscript]2ET (7), 2,4,6-( CH[subscript]3)[subscript]3C[subscript]6H[subscript]2 (8), p- C[subscript]6H[subscript]4- CH[subscript]3 (9); or R = CH[subscript]3, R[superscript]' = C[subscript]6H[subscript]5 (10)), are prepared by treating (Os(TTP)) [subscript]2 with N[subscript]2CRR[superscript]'. Complex 5 crystallizes in the space group C2/c with a = 28.003(6) A, b = 14.385(3) A, c = 33.748(8) A, [beta] = 114.51(2)[superscript]·, V = 12370(5) A[superscript]3, Z = 8, R = 4.4%, and R[subscript] w = 5.4%. The Os = C distance is 1.847(5) A. (TTP)Os(CO)(Py), (TTP)Os(Py)[subscript]2 and the carbene complexes 5-7, were found to catalyze the highly stereoselective formation of alkenes from N[subscript]2CHCO[subscript]2Et, z/e = 26, in high yield. (TTP)Os(CO)(Py) is also a stereoselective cyclopropanation catalyst for the reaction of ethyl diazoacetate with styrene, producing disubstituted cyclopropanes with a/s = 10(1). The formation of bicyclobutanes from acetylenes, and the generality of the cyclopropanation reaction to other diazoreagents and substrate alkenes is also discussed. Evidence is presented for the involvement of a trans-biscarbene in the catalytic cycle.

DOI

https://doi.org/10.31274/rtd-180813-11692

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Daniel Allen Smith

Language

en

Proquest ID

AAI9335045

File Format

application/pdf

File Size

130 pages

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