Four-Coordinate Mo(II) as (silox)₂Mo(PMe₃)₂and Its W(IV) Congener (silox)₂HW(η²-CH₂PMe₂)(PMe₃) (silox =^tBu₃SiO)

Abstract

The reduction of [( t Bu3SiO)2MoCl]2 (2 2) provided the cyclometalated derivative, (silox)2HMoMo(κ-O,C-OSi t Bu2CMe2CH2)(silox) (3), and alkylation of 2 2 with MeMgBr afforded [( t Bu3SiO)2MoCH3]2 (4 2). The hydrogenation of 4 2 was ineffective, but the reduction of 2 2 under H2 generated [( t Bu3SiO)2MoH]2 (5 2), and the addition of 2-butyne to 3 gave [(silox)2Mo]2(μ:η2η2-C2Me2) (6), thereby implicating the existence of [(silox)2Mo]2 (1 2). The addition of (silox)H to Mo(NMe2)4 led to (silox)2Mo(NMe2)2 (7), but further elaboration of the core proved ineffective. The silanolysis of MoCl5 afforded (silox)2MoCl4 (8) and (silox)3MoCl3 (9) as a mixture from which pure 8 could be isolated, and the addition of THF or PMe3 resulted in derivatives of 9 as (silox)2Cl3MoL (L = THF, 10; PMe3, 11). Reductions of 11 and (silox)2WCl4 (15) in the presence of excess PMe3 provided (silox)2Cl2MPMe3 (M = Mo, 12; W, 16) or (silox)2HW(η2-CH2PMe2)PMe3 (14). While “(silox)2W(PMe3)2” was unstable with respect to W(IV) as 14, a reduction of 12 led to the stable Mo(II) diphosphine, (silox)2Mo(PMe3)2 (17). X-ray crystal structures of 10 (pseudo-O h ), 12 (square pyramidal), and 14 and 17 (distorted T d ) are reported. Calculations address the diamagnetism of 12 and 16, and the distortion of 17 and its stability to cyclometalation in contrast to 14.

A reactive coordinatively saturated Mo(iii) complex: exploiting the hemi-lability of tris(tert-butoxy)silanolate ligands

“…This high reactivity towards N 2 reduction is unusual for an octahedral Mo( iii ) complex, and highlights the particularity of the TBOS ligand, which can adopt mono- or bidentate binding modes while being relatively small compared to larger siloxy ( e.g. t Bu 3 SiO)19 or N( t Bu) (3,5-Me 2 C 6 H 3 ) ligands 7 g…”

Activation of Carbon–Hydrogen Bonds via 1,2-RH-Addition/-Elimination to Early Transition Metal Imides

“…As Figure indicates, activation energy calculations of 1,2-MeH-elimination are generally in line with the experimentally determined, directly or indirectly, data of MeH loss from the XY­( t Bu 3 SiNH)­MMe systems, although they err to the high side. Although calculations suggested that 1,2-MeH-elimination from ( t Bu 3 SiNH)­( t Bu 3 SiN) 2 WMe ( 12 -Me) was prohibitive at Δ H ⧧ elim = 61.6 kcal/mol, the tungsten system was still interesting due to a significant enthalpy of methane binding of −15.6 kcal/mol to ( t Bu 3 SiN) 3 W ( 13 ); even the free energy of MeH binding was favorable at Δ G ° bind = −8.4 kcal/mol. ,, Three-coordinate imido species were also pyramidalized in the second and third rows in groups 5 and 6 due to n d z 2 /( n + 1)­p/( n + 1)­s mixing, − a geometric distortion favorable toward binding.…”

Niobaziridine Hydrides

“…To date, isolable examples of three-coordinate M(N[R]Ar) 3 complexes are known only for M = Ti, − V, − Cr, , and Mo; also, a uranium analogue has been isolated as its THF adduct . While the reactivity of trivalent M(N[R]Ar) 3 complexes of different periodic groups depends greatly on the d n count, reactivity differences displayed by metals of the same group are governed by a less intuitive set of properties. − This point is highlighted by Mo(N[ t -Bu]Ar) 3 , which readily effects the reductive cleavage of the dinitrogen molecule, − while its Cr analogue, Cr(N[ t -Bu]Ar) 3 , is unreactive toward N 2 under similar conditions . Accordingly, the discovery of new paradigms in small-molecule reactivity stemming from M(N[R]Ar) 3 complexes has fueled our quest to expand the library of known variants throughout the early transition elements.…”

“…( greatly on the d n count, reactivity differences displayed by metals of the same group are governed by a less intuitive set of properties. [21][22][23][24] This point is highlighted by Mo(N[t-Bu]Ar) 3 , which readily effects the reductive cleavage of the dinitrogen molecule, 4-7 while its Cr analogue, Cr(N[t-Bu]Ar) 3 , is unreactive toward N 2 under similar conditions. 18 Accordingly, the discovery of new paradigms in small-molecule reactivity stemming from M(N[R]Ar) 3 complexes has fueled our quest to expand the library of known variants throughout the early transition elements.…”

“…C{ 1 H} NMR (75.0 MHz, C 6 D 6 , 23 °C): δ 150.2 (aryl ipso amido), 149.2 (aryl ipso imido), 139.6 (o-Ar amido), 138.5 (o-Ar imido), 126.6 (p-Ar imido), 126.0 (p-Ar amido), 123.3 (m-Ar imido), 120.8 (m-Ar amido), 117.6 (enolate), 111.8 (enolate), 72.5 (N-CH2), 35.6 (C(CH 3 ) 3 anilide), 32.2 (C(CH 3 ) 3 enolate), 31.8 (C(CH 3 ) 3 enolate), 28.7 (C(CH 3 ) 3 amido), 21.9 (Ar-CH 3 amido), 21 Ad -H was prepared analogously to complex 2 Np -H employing 1.00 g (0.868 mmol) of 1 CH2Ad -I 2 and 0.454 g (1.085 mmol, 1.25 equiv) of Mg(THF) 3 (anthracene). 34 No special handling or attention to reaction time is required.…”