UC Davis

This dissertation describes the reactivity of a terphenyl-substituted heavier group 14 dimetallyne, and a diplumbyne with dinuclear transition metal carbonyls, as well as the synthesis and reactivity of certain divalent tin hydrides. The solid-state structures of the reaction products of these preparations are determined by single X-ray crystallography. Other characterization methods include nuclear magnetic resonance spectroscopy, UV-visible spectroscopy, infrared spectroscopy. A summary of the previous investigations of the synthesis and reactivity of heavy group 14 dimetallynes and the prior studies on the synthesis and reactivity of divalent tin hydrides are described in Chapter 1. Chapter 2: In this chapter, it is shown that the metathesis reactions of the diplumbyne AriPr6Pb≡PbAriPr6 (AriPr6 = −C6H3–2,6-(C6H2–2,4,6-iPr3)2) with the dinuclear metal carbonyls Mn2(CO)10, Fe2(CO)9, and Co2(CO)8 under mild conditions afford the complexes Mn(CO)5(PbAriPr6) (1), Fe(CO)4(PbAriPr6)2 (2), and Co4(CO)9(PbAriPr6)2 (3), respectively. Complexes 1–3 are structurally characterized by single-crystal X-ray diffraction and spectroscopically characterized by 1H, 13C{1H}, 59Co{1H}, and 207Pb{1H} NMR; UV–vis; and IR methods. They are rare examples of species formed by the direct reaction of a group 14 dimetallyne with transition metal carbonyls. Complexes 1 and 2 feature Mn–Pb or Fe–Pb single bonds, whereas in 3 a Co–Pb cluster is formed in which the plumbylidyne moiety bridges either an edge or a face of a Co4 carbonyl cluster. Chapter 3: In this chapter, it is shown that the reaction of the aryltin(II) hydrides {AriPr4Sn(μ-H)}2 or {AriPr6Sn(μ-H)}2 (AriPr4 = –C6H3-2,6-(C6H3-2,6-iPr2)2, AriPr6 = –C6H3-2,6-(C6H2-2,4,6-iPr3)2) with two equivalents of the molybdenum carbonyl [Mo(CO)5(THF)] yields the divalent tin hydride transition metal complexes, Mo(CO)5{Sn(AriPr6)H}, (1), or Mo(CO)5{Sn(AriPr4)(THF)H} (2), respectively. Complex 1 effects the facile hydrostannylation of carbon dioxide, to yield Mo(CO)5{Sn(AriPr6)(κ2-O,O′-O2CH)}, (3), which features a bidentate formate ligand coordinating to the tin atom. Reaction of 3 with the pinacolborane, HBpin (pin = pinacolato), in benzene regenerates 1 in quantitative yield by NMR spectroscopy. All complexes are characterized by X-ray crystallography, as well as by UV-visible, IR, and multinuclear NMR spectroscopies. The isolation of 1 and 2 is consistent with the existence of monomeric forms of {AriPr4Sn(μ-H)}2 and {AriPr6Sn(μ-H)}2 in solution. Regeneration of 1 from 3 via reaction with pinacolborane as the hydrogen source shows the catalytic potential of 1 in the hydrogenation of CO2. Chapter 4: In this chapter, it is shown that reaction of the aryltin(II) hydride {AriPr6Sn(µ-H)}2 (AriPr6 = -C6H3-2,6-(C6H2-2,4,6-iPr3)2) with two equivalents of the tungsten carbonyl THF complex, [W(CO)5(THF)], gives the divalent tin hydride transition metal complex, W(CO)5{Sn(AriPr6)H}, (1). Complex 1 reacts rapidly with ethylene, or propylene under ambient conditions to yield the corresponding hydrostannylated organometallic species, W(CO)5{Sn(AriPr6)(Et)} (2), or W(CO)5{Sn(AriPr6)(nPr)} (3), via olefin insertion into the Sn-H bond. Treatment of 1 with the Lewis base dbu (dbu = 1,8-diazabicycloundec-7-ene) yields the Lewis acid-base complex, W(CO)5{Sn(AriPr6)(dbu)H} (4), indicating that the Lewis acidity of the tin atom is preserved in 4. The complexes were characterized by X-ray crystallography, and by UV-visible, FT-IR, and multinuclear NMR spectroscopies. DFT calculations by Dr. Petra Vasko suggest hydrostannylation of ethylene with 1 proceeds via coordination of ethylene to the tin atom, then insertion into the Sn-H bond. Further computational study on the reactivity of 1 towards Ph3SiH indicated that the rate-determining step involves the metathesis reaction of a Sn-C/Si-H bond with a very high energy barrier being 71.3 kcal/mol. The calculated proton abstraction product of 1 with dbu, [W(CO)5{Sn(AriPr6)}]+[H(dbu)]-, is 18.2 kcal/mol less stable than the observed coordination product 4.