Synthesis, Crystal Structures, and Fluxional Behavior of Donor-Bridged Bis(silylene)molybdenum and -chromium Complexes

Abstract

Donor-bridged bis(silylene)molybdenum and -chromium complexes CpM(CO) 2 {(SiMe 2 )‚‚‚ Do‚‚‚(SiMe 2 )} (Cp ) η-C 5 H 5 ; M ) Mo, Do ) OMe (1a); M ) Mo, Do ) NEt 2 (1b); M ) Cr, Do ) OMe (2)) were synthesized by photolysis of a C 6 D 6 solution containing CpM(CO) 3 Me and HSiMe 2 SiMe 2 Do. The X-ray crystal structures of 1a, 1b, and 2 revealed that the M-Si bonds (2.4795(9) and 2.4804(9) Å for 1a, 2.4996(9) and 2.5008(9) Å for 1b, and 2.355(2) Å for 2) are significantly shorter than those of structurally similar silylmolybdenum and -chromium complexes, while the Si-O bonds in 1a (1.782(2) and 1.788(3) Å) and 2 (1.788(3) Å) and the Si-N bonds in 1b (1.933(2) and 1.923(3) Å) are much longer than usual Si-O and Si-N single bonds. These structural data indicate that the M-Si bonds bear partial double-bond character, whereas the Si-O and Si-N bonds are regarded as a hybrid of covalent bonding and dative bonding. The unsaturated nature of the metal-silicon bonds is also shown by the significant downfield shift of the 29 Si NMR signals (1a, δ ) 117.6 ppm; 1b, δ ) 80.5 ppm; 2, δ ) 128.6 ppm) compared to those of structurally similar silylmolybdenum and -chromium complexes. Complexes 1a, 1b, and 2 showed fluxional behavior due to silylenemethyl group exchange and, in the case of 1b, N-Et group exchange. A mechanism involving the generation of a base-free silyl(silylene) complex as the key intermediate is proposed to explain the fluxional process.

ChromiumSilicon Multiple Bonds: The Chemistry of Terminal N‐Heterocyclic‐Carbene‐Stabilized Halosilylidyne Ligands

“…The CrÀSi distance (2.2515 (7) ) is considerably shorter than that calculated for a CrÀSi single bond (2.38 ) [20] or the CrÀSi bond lengths of chromium silyl and silane complexes (2.361(2)-2.6603(8) ). [10b, 21] In addition, the Si À Br bond of 4-Br (2.4340(6) ) is considerably longer than those of metal bromosilyl complexes (2.314 ) and of bromosilanes (2.243 ).…”

Silver‐Catalyzed Silylene Transfer

“…16 Isolable early transition metal silylenoids could be synthesized by photolysis of silylmetal complexes. [18][19][20][21][22][23][24][25][26][27][28][29][30] Photolysis of iron disilyl complex 1 triggered a 1,2-silyl shift to produce a complex 2 as a 2 : 1 mixture of diastereomers (Scheme 7.1). 19 Ogino and coworkers interpreted the nearly planar relationship of the atoms at each silicon and the short Fe--Si bonds (2.207 and 2.222 A ) as evidence of bis(silylene) character.…”

A DFT study on geometric preference of non-bridging form to bridging form in molybdenum complexes with phosphenium ligand

“…Similar dihedral angle for C(6)e Mo(1)eP(11)eN(18) in 1_LM1 between the X-ray structure and the calculated value means that the structure in solid state is similar to 1_LM1. The P(10)eMo(1)eP (11) angle in the bridging form 1_TS2 is smaller by 22.6 than that in the non-bridging form as already pointed out [2]. The PeP distance concomitantly decreases by 0.677 Å.…”

“…Therefore, Si1_LM1 could be easily converted to Si1_LM2 by its rotation. Ogino and his coworkers had estimated the activation energy from Si1_LM2 to Si1_LM1 as 15.6 kcal/mol [11], which is smaller than the calculated value (21.07 þ 1.75 ¼ 22.82 kcal/mol) by 7.2 kcal/mol. Bi and his coworkers reported mechanistic study on the ring-opening of alkoxy-bridging silylene complex.…”