Synthesis and Characterization of DMAP-Stabilized Aryl(silylene) Complexes and (Arylsilyl)(DMAP) Complexes of Tungsten: Mechanistic Study on the Interconversion between These Complexes via 1,2-Aryl Migration

Abstract

Photoreaction of a mixture of Cp*(CO) 3 WMe (Cp* ) η 5 -C 5 Me 5 ) and HSiR 2 Ar [R 2 Ar ) Me 2 Ph, Me 2 (p-Tol), Me(p-Tol) 2 , and (p-Tol) 3 ] in the presence of 4-(dimethylamino)pyridine (DMAP) gave DMAPstabilized aryl(silylene) complexes Cp*migration of the aryl group from a silyl ligand to a tungsten center. Thermal reactions of Cp*(CO) 2 W(DMAP)Me (2) with HSiR 2 Ar at room temperature also gave 1a-d, and in all cases the yields were higher than those in the photoreaction. Silylene complexes 1a-d easily isomerized to arylsilyl complexes Cp*(CO) 2 -W(DMAP)(SiR 2 Ar) [3a, R ) Me, Ar ) Ph; 3b, R ) Me, Ar ) p-Tol; 3c, R 2 ) Me(p-Tol), Ar ) p-Tol; 3d, R ) Ar ) p-Tol] at 40-55 °C. On the other hand, irradiation of arylsilyl complexes 3a-d reproduced silylene complexes 1a-d, implying that the 1,2-aryl-migration between tungsten and silicon is reversible. The molecular structures of 1c, 2, 3a, and 3d were determined by X-ray crystallography. A kinetic study on the 1,2-aryl-migration in the thermal isomerization from 1a-d to 3a-d suggests that the rate-determining step involves dissociation of DMAP from 1a-d.

Reactions of Hydrosilanes with Transition Metal Complexes

“…Heating gives the thermodynamic product which results from rearrangement to Cp*­(OC) 2 W­(DMAP)­(SiMe 2 Ph) for 5-23a (analogs of the others also prepared; X-ray of product from HSi­( p -Tol) 3 has been previously reported). Complexes were also prepared from the photoreaction of a mixture of Cp*­(OC) 3 WMe and HSiR 2 Ar . Photolysis of the thermodynamic product produces the silylene complex …”

“…Complexes were also prepared from the photoreaction of a mixture of Cp*­(OC) 3 WMe and HSiR 2 Ar . Photolysis of the thermodynamic product produces the silylene complex 20 Ar′ = 2,6-dimethylphenyl; Ar = 2,6- i Pr 2 C 6 H 3 .…”

“…Tobita and co-workers published four papers, three with tungsten silylenes ,, and one with a ruthenium silylene, but all prepared by the same basic approach that involved migration of a substituent on silicon to the metal center. The tungsten silylenes are summarized in Scheme and the ruthenium silylene in eq 55 .…”

“… 11 Other Derivatives: Cr : 2.1603(7); 2.1618(9); 2.2515(7); 2.2847(6); 2.326­(av); 2.329­(av); 2.3398(4); 2.3458(7); 2.515(7); Mo: 2.2241(7); 2.287(1) (dble); 2.300(1) (dble); 2.3430(6); 2.3474(6); 2.471­(av); 2.4550(14); 2.4562(16); 2.480­(av); 2.480(2); 2.4883(8); 2.5125(7); 2.5135(9); 2.515(2); 2.5172(8); 2.519(4); 2.5221(9); 2.5231(19); 2.546(2); 2.5536(13); 2.554(5); 2.5552(17); 2.584(3); 2.608; 2.6178(6); 2.624(3); 2.624; 2.632; 2.634(3); 2.6491(3); 2.654; 2.6659(7); 2.6675(17); 2.9647(8); 247 3.2204(9); 3.4394(10); (last 3 are considered nonbonding). W: 2.376­(dble); 2.3760(9); 2.386; 2.4202(14) (dble); 2.4562(16); 2.471­(av); 2.4990(8); 2.5086(11); 2.5125(7); 2.5257(12); 2.5474(16) (av of 2); 2.573(4); 2.5991(13); 2.608; 2.6110(13); 2.615(2); 2.620(8); 2.625(2); 2.6399(14); 2.6512(7); 2.6778(10) 12 Hydrogens were found in the difference Fourier map and refined isotropically …”

Cooperativity in Transition Metal Tetrylene Complexes

“…As a first step to demonstrating migration with larger groups, the Tobita group investigated 1,2‐methyl and 1,2‐aryl migration from W to Si in a range of silylenes. [ 62 , 63 , 64 , 65 ] Work on reversible aryl migrations, which is summarised in Scheme 9 , resulted in the isolation of the aryl migration intermediate – a silicon analogue of an η 3 ‐benzyl complex ( 26 ) – for both W and Mo. [ 64 , 65 ]…”