Reactions of nitriles RCN with the sterically encumbered Mo(N[t-Bu]Ar)3 (1, Ar = 3,5-C6H3Me2) or the somewhat less hindered Mo(H)(η2-Me2CNAr)(N[i-Pr]Ar)2 (2) have been investigated. Where R = Me or Ph, reaction with 1 results in reductive nitrile coupling and the formation of a diiminato product [μ-NC(R)C(R)N][1]2. In contrast, reaction of 1 with Me2NCN surprisingly results in a stable, albeit highly congested, η2 adduct of the nitrile. When the less sterically hindered 2 is used, reaction with PhCN gives the diiminato product analogous to the one mentioned for the tert-butyl system, [μ-NC(Ph)C(Ph)N][Mo(N[i-Pr]Ar)3]2, where molybdaziridine-hydride 2 has provided access to the three-coordinate Mo(N[i-Pr]Ar)3 (3) moiety. Use of a more bulky nitrile such as MesCN (Mes = 2,4,6-C6H2Me3) results in formation of a bis-η1 compound, (η1-MesCN)2[3]. Use of 9-anthracenylcarbonitrile results in head-to-tail C−C coupling of two monomers via the anthracenyl moiety. Detailed variable-temperature EPR and 2H NMR data are included for both molybdenum-containing starting materials and selected reaction intermediates and products.

Enthalpies of chalcogen atom transfer to Mo(N[t-Bu]Ar)3, where Ar = 3,5-C6H3Me2, and to IPr (defined as bis-(2,6-isopropylphenyl)imidazol-2-ylidene) have been measured by solution calorimetry leading to bond energy estimates (kcal/mol) for EMo(N[t-Bu]Ar)3 (E = S, 115; Se, 87; Te, 64) and EIPr (E = S, 102; Se, 77; Te, 53). The enthalpy of S-atom transfer to PMo(N[ t-Bu]Ar) 3 generating SPMo(N[t-Bu]Ar)3 has been measured, yielding a value of only 78 kcal/mol. The kinetics of combination of Mo(N[t-Bu]Ar)3 with SMo(N[t-Bu]Ar)3 yielding (mu-S)[Mo(N[t-Bu]Ar)3]2 have been studied, and yield activation parameters Delta H (double dagger) = 4.7 +/- 1 kcal/mol and Delta S (double dagger) = -33 +/- 5 eu. Equilibrium studies for the same reaction yielded thermochemical parameters Delta H degrees = -18.6 +/- 3.2 kcal/mol and Delta S degrees = -56.2 +/- 10.5 eu. The large negative entropy of formation of (mu-S)[Mo(N[t-Bu]Ar)3]2 is interpreted in terms of the crowded molecular structure of this complex as revealed by X-ray crystallography. The crystal structure of Te-atom transfer agent TePCy3 is also reported. Quantum chemical calculations were used to make bond energy predictions as well as to probe terminal chalcogen bonding in terms of an energy partitioning analysis.

The placement of a strongly trans-influencing ligand on a ruthenium center opposite an anchoring silyl group of the tetradentate tripodal tris(phosphino)silyl ligand, [SiP Ph 3 ] -([SiP Ph 3 ] -=tris(2-(diphenylphosphino)phenyl)silyl), has been explored. Installation of alkyl or terminal phosphide ligands trans to the anchoring silyl group affords the complexes [SiP Ph 3 ]RuR (R=Me (2), CH 2 Ph (4), PPh 2 (5), P i Pr 2 ( 6)). Complexes 2, 4, and 5 are thermally unstable. Complexes 2 and 4 decay to the cyclometalated complex [SiP Ph 2 P 0Ph ]Ru (3), whereas complex 5 decays to the cyclometalated phosphine adduct [SiP Ph 2 P 0Ph ]Ru-(PHPh 2 ) (7). Complex 3 is found to effect E-H (E=H, C, Si, Ge) bond activation of substrates such as secondary silanes and germanes to yield the structurally unusual silylene complexes [SiP Ph 3 ]Ru(H) (SiRR 0 ) (R=R 0 =Ph (10a), R=Ph R 0 =Me (10b)) and the germylene complex [SiP Ph 3 ]Ru(H)(GeR 2 ) (R = Ph) (11) via double E-H activation transformations. Both theory and experiments suggest electrophilic character at the silylene moiety. Reaction of 3 with catecholborane, in contrast to silanes and germanes, results in insertion of the B-H unit into the M-C bond of the cyclometalated species to yield the borate complex [SiP Ph 2 P Ph -B(cat)]Ru(μ-H) ( 14). Complex 3 also reacts with bis(catecholato) diboron to yield a similar complex, [SiP Ph 2 P C6H3B(cat) -B(cat)]Ru(μ-H) (15), with selective borylation of an ortho C-H bond.