Wm. Vaughan et al., SYNTHESIS AND REACTIVITY OF TRIS(PYRAZOLYL)BORATE-STABILIZED MOLYBDENUM IMIDO ALKYLIDENE COMPLEXES, Organometallics, 14(4), 1995, pp. 1567-1577
The addition of LiCH3 to TpMo(CHR)(NAr)(OTf) (1; Tp = hydridotris(1-py
razolyl)borate; R = C(CH3)(2)Ph; Ar = 2,6-i-Pr-C6H3; OTf = OSO2(CF3))
gave TpMO(CHR)(NAr)(CH3) (2). Compound 2 was used to prepare several s
olvent-bound, cationic complexes by abstracting the methyl ligand. The
addition of tetrakis(3,5-bis(trifluoromethyl)phenyl)boric acid to 2 i
n Et(2)O gave [TpMo(CHR)(NAr)(Et(2)O)][BAr'(4)] (3; Ar' = 3,5-C6H3(CF3
)(2)) and CH4. The reaction of 2 and trityl tetrakis(pentafluorophenyl
)borate in the presence of excess acetonitrile gave [TpMo(CHR)(NAr)(NC
CH3)][B(C6F5)(4)] (4) and Ph(3)CCH(3). The Lewis acid B(C6F5)(3) abstr
acted the methyl ligand of 2 in the presence of acetonitrile or tetrah
ydrofuran to give the compounds [TpMo(CHR)(NAr)(S)][B(CH3)(C6F5)(3)] (
5, S = NCCH3; 6, S = THF). The triflate ligand of 1 was displaced by t
rimethylphosphine to give [TpMo(CHR)(NAr)(P(CH3)(3))][OTf] (7). Stirri
ng 1 in the presence of methanol and Florisil gave TpMo(CHR)(NAr)(OCH3
) (8). The addition of excess potassium methoxide to 1 gave TpMo(CR)(N
HAr)(OCH3) (9). Attempts to convert 8 to 9 by heating, photolysis, and
the addition of NEt(3) or PMe(3) were unsuccessful. Since only excess
methoxide converts 8 to 9, a methoxide-mediated proton transfer mecha
nism is proposed. X-ray structures of syn-8 (P2(1)2(1)2(1), a = 12.620
(2) Angstrom, b = 13.492(2) Angstrom, c = 19.682(2) Angstrom, Z = 4, V
= 3351.3(7) Angstrom(3), M(r) = 647.48, d(calc) = 1.283 g/cm(3), R =
6.00%, R(w) = 5.89%) and syn-9 (P ($) over bar 1, a = 10.624(2) Angstr
om, b = 11.766(2) Angstrom, c = 13.980(2) Angstrom, alpha = 86.96(2)de
grees, beta = 86.54(2)degrees, gamma = 67.77(2)degrees, Z = 2, V = 163
5.8(7) Angstrom(3), M(r) = 647.48, d(calc) = 1.283 g/cm(3), R = 4.84%,
R(w) = 4.87%) were obtained, and a trans-influence series has been es
tablished for several ligands. Rotational isomers due to rotation abou
t the Mo-alkylidene bond were observed for all compounds, and marked d
ifferences in rates of rotamer interconversion are observed for 1, 2,
and 8. Compounds 1 and 2 in the presence of AlCl3 successfully catalyz
ed the ring-opening metathesis polymerization of cyclooctene and norbo
rnylene and the oligomerization of 1,9-decadiene via acyclic diene met
athesis polymerization.