We report the first mononuclear three-coordinate vanadium(II) complex [(nacnac)V(ODiiP)] and its activation of N2 to form an end-on bridging dinitrogen complex with a topologically linear V(III)N2V(III) core and where each vanadium center antiferromagnetically couples to give a ground state singlet with an accessible triplet state as inferred by HFEPR spectroscopy. In addition to investigating the conversion of N2 to the terminal nitride (as well as the microscopic reverse process), we discuss its similarities and contrasts to the isovalent d(3) system, [Mo(N[(t)Bu]Ar)3], and the S = 1 system [(Ar[(t)Bu]N)3Mo]2(μ2-η(1):η(1)-N2).

Triphenylsiloxide is one of the most successful ancillary ligands for Mo­(VI)-alkyne metathesis catalysts. It was proposed that flexible siloxide ligands allow Mo–O–Si bond angles to modulate the electrophilicity of MoC and thereby promote the catalysis. Introduction of a siloxide podand ligand allowed elucidation of the effect of ligand flexibility and Mo–O–Si angles on the electrophilicity of MoC. It also allowed for the isolation of a rare metallatetrahedrane of Mo­(VI) which was found to be dynamic in solution.

The intermediacy of metallacyclobutadienes as part of a [2 + 2]/retro-[2 + 2] cycloaddition-based mechanism is a well-established paradigm in alkyne metathesis with alternative species viewed as off-cycle decomposition products that interfere with efficient product formation. Recent work has shown that the exclusive intermediate isolated from a siloxide podand-supported molybdenum-based catalyst was not the expected metallacyclobutadiene but instead a dynamic metallatetrahedrane. Despite their paucity in the chemical literature, theoretical work has shown these species to be thermodynamically more stable as well as having modest barriers for cycloaddition. Consequentially, we report the synthesis of a library of group VI alkylidynes as well as the roles metal identity, ligand flexibility, secondary coordination sphere, and substrate identity all have on isolable intermediates. Furthermore, we report the disparities in catalyst competency as a function of ligand sterics and metal choice. Dispersion-corrected DFT calculations are used to shed light on the mechanism and role of ligand and metal on the intermediacy of metallacyclobutadiene and metallatetrahedrane as well as their implications to alkyne metathesis.

Deprotonation of the parent titanium imido ((tBu)nacnac)Ti≡NH(Ntolyl2) ((tBu)nacnac(-) = [ArNC(t)Bu]2CH; Ar = 2,6-(i)Pr2C6H3) with KCH2Ph forms a rare example of a molecular titanium nitride as a dimer, {[K][((tBu)nacnac)Ti≡N(Ntolyl2)]}2. From the parent imido or nitride salt, the corresponding aluminylimido-etherate adduct, ((tBu)nacnac)Ti≡N[AlMe2(OEt2)](Ntolyl2), can be isolated and structurally characterized. The parent imido is also a source for the related borylimido, ((tBu)nacnac)Ti═NBEt2(Ntolyl2).

The four-coordinate zinc compound ToMZnH (1, ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate) catalyzes selective alcoholysis of substituted hydrosilanes. The catalytic reaction of PhMeSiH2 and aliphatic alcohols favors the monodehydrocoupled product PhMeHSi-OR. With the aryl alcohol 3,5-C6H3Me2OH, the selectivity for mono(aryloxy)hydrosilane PhMeHSiOC6H3Me2 and bis(aryloxy)silane PhMeSi(OC6H3Me2)2 is controlled by relative reagent concentrations. Reactions of secondary organosilanes and diols provide cyclic bis(oxo)silacycloalkanes in high yield. The empirical rate law for the ToMZnH-catalyzed reaction of 3,5-dimethylphenol and PhMeSiH2 is −d[PhMeSiH2]/dt = k′obs [ToMZnH]1 [3, 1,2 Our interest in the catalytic preparation of alkoxysilanes was inspired by our interactions with Prof. Victor Lin, as we sought to synthesize precursors for advanced silica-based functionalized nanomaterials for catalytic applications. Silyl ethers are also important building blocks in organosilicon chemistry and in synthetic organic chemistry as protecting groups.3 The reaction of chlorosilanes and alcohols provides a straightforward route to SiÀO bonds. However, the HCl byproduct of these reactions must be trapped with base, and this method is not useful for syntheses that require neutral conditions. The degree of condensation is difficult to control when more than one SiÀCl group is present in the silicon substrate. Furthermore, chlorosilanes are water sensitive and must be kept rigorously anhydrous prior to use. Catalytic SiÀH bond alcoholysis (eq 1) can avoid these problems, giving H 2 as the byproduct and bypassing acid formation and/or basic conditions. Organosilanes are not hydrolytically sensitive (in the absence of a catalyst), and catalysts can control selectivity. -hydrosilane or silyl hydride transition-metal complexes formed via oxidative addition steps. 7,13,14 In contrast, copperand gold-catalyzed silane alcoholyses are proposed to involve discrete metal hydride and metal-alkoxide intermediates (no MÀSi bond). 18,20 In situ generated zinc(II) catalysts are also proposed to follow this mechanism.23 However, these zinc, copper, and gold catalysts are generated in situ, the catalytic speciation is unknown, and the turnover-limiting step has not been established.Zinc(II) catalysts are particularly interesting, given the low cost, favorable biocompatibility, and high natural abundance of this main group metal. Although zinc hydrides are presumed intermediates in hydrosilane alcoholysis, the catalytic activity of the few isolable, monomeric, terminal zinc hydrides is not developed. 24À28