Versatile Tautomerization of EH₂-Substituted Silylenes (E = N, P, As) in the Coordination Sphere of Nickel

Abstract

The synthesis and tautomerization of a "halfparent" aminosilylene and its heavy P-and As-analogues ( TMS LSi-EH 2 ; E = N, P, As; TMS L = N(SiMe 3 )(2,6-i Pr 2 C 6 H 3 )) in the coordination sphere of nickel(0) to give the corresponding side-on η 2 -RSi(H)EH and RH 2 Si-E ("silylpnictinidene") nickel complexes are reported. These complexes can be accessed through salt metathesis reactions of the lithium dihydropnictides LiEH 2 with the acyclic chlorosilylene nickel(0) complex 1, [ TMS L(Cl)Si → Ni(NHC) 2 ; NHC = :C[( i Pr)NC(Me)] 2 ). In addition, we report the facile E−H bond activation reactions of EH 3 with 1, which furnished a silyl nickel(II) complex through NH 3 activation, but phosphido and arsenido complexes in the activation of PH 3 and AsH 3 , respectively. Notably, reaction of 1 with LiNH 2 leads to the acyclic bis(amido)silylene complex [ TMS L(H 2 N)Si → Ni(NHC) 2 ] 5, which does not undergo N−H proton migration to silicon(II) under ambient conditions. The transformation of the P-and As-analogues of 1 furnishes directly the respective side-on SiE Ni complexes (nickelacycles), [η 2 -{ TMS L(H)Si E(H)}Ni(NHC) 2 ] (E = P, 6; E = As, 9). These nickelacycles show a vastly different stability in solutions. While 6 is stable for several days at ambient temperature, 9 undergoes further rearrangement processes within minutes of its formation. Given the high acidity of the As−H proton in 9, however, this moiety can be trapped as a highly charge separated metalated-η 2 -silaarsene nickel complex 12 that is best described as an [AsSiNi] nickelacycle with Si−As multiple bond character. Taken as a whole, these results give, for the first time, insights into the relative stability of the tautomeric forms of side-on silaldimine transition metal complexes. The electronic nature and the rearrangement processes of these compounds were also investigated by quantum chemical calculations.

Molecular Main Group Metal Hydrides

“… In 2019, Driess and coworkers demonstrated a direct route to [Li­(TMEDA)]­[AsH 2 ] by exposure of a solution of n BuLi/TMEDA mixture to arsine gas. This may prove a convenient source of [AsH 2 ] − due to the reported solubility of [Li­(TMEDA)]­[AsH 2 ] in Et 2 O, THF and toluene, unlike the commonly used donor-free salts such as K­[AsH 2 ] . This soluble arsenide was then combined with the silylene nickel(0) complex [(ImMe 2 i Pr 2 ) 2 Ni–Si­(Cl)­{N­(Dipp)­SiMe 3 }] ( 1250 ) in THF, forming a thermally unstable reaction mixture.…”

Cooperativity in Transition Metal Tetrylene Complexes

“…Bond activation of NH 3 , PH 3 , and AsH 3 was also achieved at 6 , and investigation of further rearrangements provided the first evidence for the tautomerisation between silylene‐silapnictene‐silylpnictinidene compounds, a new class of main group‐transition metal complexes. [46] A somewhat related H−H activation was found at a bis‐silylene Ni(0) complex that was also an efficient hydrogenation catalyst. [48] …”

“…Low‐valent nickel silylenes have been investigated by the Driess group in the context of E−H bond cleavage and the synthesis of heavier analogues of η 2 ‐alkene complexes [45–47] . First, irreversible cleavage of dihydrogen at complex 6 to form nickel silyl complex 7 was observed.…”

“…Low‐valent nickel silylenes have been investigated by the Driess group in the context of E−H bond cleavage and the synthesis of heavier analogues of η 2 ‐alkene complexes. [ 45 , 46 , 47 ] First, irreversible cleavage of dihydrogen at complex 6 to form nickel silyl complex 7 was observed. The mechanism was proposed to occur in a manner similar to that of Pt complex 1 ; that is, nickel‐centred oxidative addition of dihydrogen followed by migration of a H atom to the silicon centre (Scheme 2 ).…”

Taming PH3: State of the Art and Future Directions in Synthesis

“…123 Driess has further elaborated the silylene chemistry of PH 3 58 by taking a nickel-silylene species and demonstrating the coordination chemistry of PH 2 (derived from Li(dme)PH 2 or Li(tmeda)PH 2 ), generating 36 (Scheme 24) and subsequent isomerization chemistry of the η 2 -species to generate 37/38. 124 Finally, Scheer has also employed NaPH 2 to generate a Mo dimer with a mixed P/As bridge (39, Scheme 25). 125 A fundamental study, but one where we can envisage links to higher order main group polymer chains 126 with unique properties.…”