We demonstrate that a titanium-carbon multiple bond, specifically an alkylidyne ligand in the transient complex, (

Addition of organic azides, N(3)R (R = 2,4,6-trimethylphenyl (Mes), phenyl (Ph), 1-adamantyl (Ad)), to a solution of the uranium(III) alkyl complex, Tp*(2)U(CH(2)Ph) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) (1), results in the formation of a family of uranium(iv) imido derivatives, Tp*(2)U(NR) (2-R). Notably, these complexes were synthesized in high yields by coupling of the benzyl groups to form bibenzyl. The uranium(IV) imido derivatives, 2-Mes, 2-Ph, and 2-Ad, were all characterized by both (1)H NMR and IR spectroscopy, and 2-Mes and 2-Ad were also characterized by X-ray crystallography. In the molecular structure of 2-Mes, typical κ(3)-coordination of the Tp* ligands was observed; however in the case of 2-Ad, one pyrazole ring of a Tp* ligand has rotated away from the metal centre, forcing a κ(2)-coordination of the pyrazoles. This results in a uranium-hydrogen interaction with the Tp* B-H. Treating these imido complexes with para-tolualdehyde results in multiple bond metathesis, forming the terminal uranium(IV) oxo complex, Tp*(2)U(O), and the corresponding imine.

The transient titanium alkylidyne, (PNP)Tit C t Bu (PNP = N[2-P i Pr 2 -4-methylphenyl] 2 À ), activates a CÀ H bond of ethane at room temperature, and a β-hydrogen of the resulting ethyl ligand is subsequently transferred to the adjacent alkylidene ligand to form an ethylene adduct of titanium. Treatment of the ethylene complex with twoelectron oxidants such as organic azides results in extrusion of ethene concomitant with formation of a mononuclear titanium imido complex.

The transient titanium neopentylidyne, [(PNP)Ti≡C(t)Bu] (A; PNP(-)≡N[2-P(i)Pr2-4-methylphenyl]2(-)), dehydrogenates ethane to ethylene at room temperature over 24 h, by sequential 1,2-CH bond addition and β-hydrogen abstraction to afford [(PNP)Ti(η(2)-H2C═CH2)(CH2(t)Bu)] (1). Intermediate A can also dehydrogenate propane to propene, albeit not cleanly, as well as linear and volatile alkanes C4-C6 to form isolable α-olefin complexes of the type, [(PNP)Ti(η(2)-H2C═CHR)(CH2(t)Bu)] (R = CH3 (2), CH2CH3 (3), (n)Pr (4), and (n)Bu (5)). Complexes 1-5 can be independently prepared from [(PNP)Ti═CH(t)Bu(OTf)] and the corresponding alkylating reagents, LiCH2CHR (R = H, CH3(unstable), CH2CH3, (n)Pr, and (n)Bu). Olefin complexes 1 and 3-5 have all been characterized by a diverse array of multinuclear NMR spectroscopic experiments including (1)H-(31)P HOESY, and in the case of the α-olefin adducts 2-5, formation of mixtures of two diastereomers (each with their corresponding pair of enantiomers) has been unequivocally established. The latter has been spectroscopically elucidated by NMR via C-H coupled and decoupled (1)H-(13)C multiplicity edited gHSQC, (1)H-(31)P HMBC, and dqfCOSY experiments. Heavier linear alkanes (C7 and C8) are also dehydrogenated by A to form [(PNP)Ti(η(2)-H2C═CH(n)Pentyl)(CH2(t)Bu)] (6) and [(PNP)Ti(η(2)-H2C═CH(n)Hexyl)(CH2(t)Bu)] (7), respectively, but these species are unstable but can exchange with ethylene (1 atm) to form 1 and the free α-olefin. Complex 1 exchanges with D2C═CD2 with concomitant release of H2C═CH2. In addition, deuterium incorporation is observed in the neopentyl ligand as a result of this process. Cyclohexane and methylcyclohexane can be also dehydrogenated by transient A, and in the case of cyclohexane, ethylene (1 atm) can trap the [(PNP)Ti(CH2(t)Bu)] fragment to form 1. Dehydrogenation of the alkane is not rate-determining since pentane and pentane-d12 can be dehydrogenated to 4 and 4-d12 with comparable rates (KIE = 1.1(0) at ~29 °C). Computational studies have been applied to understand the formation and bonding pattern of the olefin complexes. Steric repulsion was shown to play an important role in determining the relative stability of several olefin adducts and their conformers. The olefin in 1 can be liberated by use of N2O, organic azides (N3R; R = 1-adamantyl or SiMe3), ketones (O═CPh2; 2 equiv) and the diazoalkane, N2CHtolyl2. For complexes 3-7, oxidation with N2O also liberates the α-olefin.

Heteroleptic copper(I) complexes of the types [Cu(N,N)(P,P)] and [Cu(N,O)(P,P)], where (P,P) = phosphine (PPh(3)) or diphosphine (dppb, DPEPHOS, XANTPHOS), (N,N) = pyrrole-2-phenylcarbaldimine, 2PyN: [Cu(2PyN)(PPh(3))(2)] (1), [Cu(2PyN) (dppb)] (2), [Cu(2PyN)(DPEPHOS)] (3), and [Cu(2PyN)(XANTPHOS)] (4), (N,N) = indole-2-phenylcarbaldimine, 2IndN: [Cu(2IndN)(DPEPHOS)] (8), and (N,O) = pyrrole-2-carboxaldehyde, 2PyO: [Cu(2PyO)(DPEPHOS)] (5), [Cu(2PyO)(XANTPHOS)] (6), or (N,O) = indole-2-carboxaldehyde, 2IndO: [Cu(2IndO)(DPEPHOS)] (7), were synthesized and characterized by multinuclear NMR spectroscopy, electronic absorption spectroscopy, fluorescence spectroscopy, and X-ray crystallography (1-3, 5-8). The complexes with aldimine ligands are thermally stable, and sublimation of 2-4 was possible at T = 230-250 °C under vacuum. All complexes exhibit long-lived emission in solution, in the solid state, and in frozen glasses. The excited states have been assigned as mixed intraligand and metal-to-ligand charge transfer (3)(MLCT + π-π*) transitions through analysis of the photophysical properties and DFT calculations on representative examples.