Reactivity studies of a rare example of a molecular titanium nitride are presented. A combination of theory and NMR spectroscopy provide a description of the bonding in the these nitrides, the role of the counter cation, K+, as well as the origin of their highly downfield 15N NMR spectroscopic shifts.

A quinoline-derived titanium complex (TiQ) is shown here to possess remarkable photosensitizing properties when treated with an iodonium salt (Iod) to initiate, under visible light irradiation, (i) the free-radical photopolymerization of acrylate monomer in aerated/laminate conditions, (ii) the cationic photopolymerization of epoxy monomer under air, and (iii) the in situ formation of Ti-based nanoparticles (NPs) inside coatings. The photochemical properties of the TiQ/Iod photoinitiating system have been probed by electron paramagnetic resonance, laser flash photolysis, and real-time Fourier transform infrared spectroscopy, which provide an insight into the possible radical/cationic pathways. The microstructural properties of the photosynthesized Ti-based NPs have been investigated by bright-field conventional transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy. The macroscopic mechanical properties of the resulting nanocomposite reveal that the generation of these Ti-based NPs in a polyacrylate/polyether blend matrix leads to an increase of mechanical resistance by toughening the matrix.

Complex (PNP)Nb(CH3)2(OAr) (PNP = N[2-P(i)Pr2-4-methylphenyl]2(-), Ar = 2,6-(i)Pr2C6H3), prepared from treatment of (PNP)NbCl3 with NaOAr followed by 2 equiv of H3CMgCl, can be oxidized with [FeCp2][OTf] to afford (PNP)Nb(CH3)2(OAr)(OTf). While photolysis of the latter resulted in formation of a rare example of a niobium methylidene, (PNP)Nb═CH2(OAr)(OTf), treatment of the dimethyl triflate precursor with the ylide H2CPPh3 produced the mononuclear group 5 methylidyne complex, (PNP)Nb≡CH(OAr). Adding a Brønsted base to (PNP)Nb═CH2(OAr)(OTf) also resulted in formation of the methylidyne. Solid-state structural analysis confirms both methylidene and methylidyne moieties to be terminal, having very short Nb-C distances of 1.963(2) and 1.820(2) Å, respectively. It is also shown that methylidyne for nitride cross-metathesis between (PNP)Nb≡CH(OAr) and NCR (R = tert-butyl or 1-adamantyl) results in formation of a neutral and mononuclear niobium nitride, (PNP)Nb≡N(OAr), along with the terminal alkyne HC≡CR.

A series of nitrogen K-edge XAS data obtained for coordination complexes of diverse transition metals is used to calibrate computational pre-edge peak energies and to afford estimates of metal–ligand covalencies. The approach is extended to probe an inner-sphere aminyl radical ligand.

Selectively converting linear alkanes to α-olefins under mild conditions is a highly desirable transformation given the abundance of alkanes as well as the use of olefins as building blocks in the chemical community. Until now, this reaction has been primarily the remit of noble-metal catalysts, despite extensive work showing that base-metal alkylidenes can mediate the reaction in a stoichiometric fashion. Here, we show how the presence of a hydrogen acceptor, such as the phosphorus ylide, when combined with the alkylidene complex (PNP)Ti=CHBu(CH) (PNP=N[2-P(CHMe)-4-methylphenyl]), catalyses the dehydrogenation of cycloalkanes to cyclic alkenes, and linear alkanes with chain lengths of C to C to terminal olefins under mild conditions. This Article represents the first example of a homogeneous and selective alkane dehydrogenation reaction using a base-metal titanium catalyst. We also propose a unique mechanism for the transfer dehydrogenation of hydrocarbons to olefins and discuss a complete cycle based on a combined experimental and computational study.

The mononuclear niobium methylidyne [(PNP)­(ArO)­NbCH] (1; PNP– = N­[2-P i Pr2-4-methylphenyl]2 –, Ar = 2,6- i Pr2C6H3) reacts with the isocyanate OCN t Bu to form a mononuclear niobium oxo species with a rare example of an azaallenyl ligand, namely [(PNP)­(ArO)­NbO­(CHCN t Bu)] (2). When 1 is treated with the phosphaalkyne PCAd (Ad = 1-adamantyl), PC bond cleavage occurs to form a mononuclear complex where P–P coupling has occurred between the formal phosphaalkyne phosphorus atom and one phosphine arm from the PNP ligand, namely [(PNPP)­(ArO)­Nb­(η2-AdCCH)] (3). Solid-state structural studies and isotopic labeling experiments confirm C–C bond formation of the methylidyne group as well as provide conclusive evidence for the oxo ligand in 2 being terminal and the fate of the phosphorus atom from PCAd in complex 3. Computational studies have been applied to understand the pathway involving the P–P bond forming reaction of 1 and PCAd.

Niobium methylidyne [(PNP)­NbCH­(OAr)] (1) (PNP– = N­[2-P i Pr2-4-methylphenyl]2 –, Ar = 2,6- i Pr2C6H3) reacts with excess ethylene to afford the propenyl-ethylene complex [(PNP)­Nb­(HCCHCH3)­(η2-H2CCH2)­(OAr)] (2), which, upon gentle heating, extrudes ethylene to yield a low-spin Nb­(III) allyl complex [(PNP)­Nb­(η3-H2CCHCH2)­(OAr)] (3). Isotopic labeling studies using [(PNP)­Nb13CH­(OAr)] (1- 13 C) have allowed us to not only observe and propose the formation of various intermediates in the conversion of 1 to 2 and then 3 but also demonstrate scrambling of the CH2 groups to only the terminal positions of the allyl moiety. The homologation of ethylene to a propenyl or isomeric allylic group might help explain why complex 1 is an inefficient catalyst for the ring-opening expansion polymerization of 2-norbornene to cyclic polynorbornene.

C–H activation of methane followed by dehydrocoupling at room temperature led ultimately to the formation of the olefin H2CCHtBu via the addition of redox-active ligands (L) such as thioxanthone or 2,2′-bipyridine (bipy) to (PNP)TiCHtBu(CH3) (1).