No abstract

overall configuration at the Mn( 1) center is also remarkable. Both the amide bonds are on one side of the manganese (cis) with an angle of 127.1 (3)O between them. This unusual coordination is, in some respects, reminiscent of the coordination seen in the metal borylamides M(NArBMes,), ( M = Cr-Ni; Ar = Ph or Mes)."J3*12' The metal coordination in these molecules is also 2-fold, but secondary interactions are observed between the metal and an ipso carbon of a boron-mesityl group so that cis structures very similar to that seen in 7 are observed. This is especially true for the Cr and Mn complexes. Another interesting feature of this structure is that if the weak coordination to N(2) is taken into account, the resulting four-coordinate structure is closer to planar coordination than it is to tetrahedral coordination. This is because the angle between the Mn(l)N(l)N(2) and Mn( l)N(la)N(2a) planes is only 35.4O. This observation is difficult to explain since the structure is quite crowded. This crowding is evident in the (27) Bartlett, R. A.; Chen, H.; Power, P. P. Angew. Chem., Int. Ed. Engl. 1989, 28, 316.bending of the aromatic rings away from each other. For example, there is an angle of 8.2O between the N(l)-C(3) bond and the plane of the C(3) phenyl ring, and an angle of 5 . 5 O is observed between the N(2)-C( 15) bond and the C( 15) ring plane. This congestion might have been relieved by the adoption of a trans geometry at Mn( 1) or by dispensing with the coordination of one or both of the N(2) atoms. The structure of 7 is apparently a comprise between these competing factors. Experiments on these and related ligands and their transition-metal complexes is continuing.Acknowledgment. We thank the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this work.Supplementary hhterial Available: Tables giving full details of X-ray data collection and refinement and complete atom coordinates, bond distances and angles, hydrogen coordinates, and anisotropic thermal parameters and a drawing of the second molecule of 3 in the asymmetric unit (34 pages). Ordering information is given on any current masthead page. Adducts of (silox),M (M = Ta (I), Ti (2), Sc (3), V (4)) have been prepared in order to assess the various electronic factors responsible for qi-pyridine4 vs. q2-pyridine-N,C ligation. Treatment of ScCI,(THF), or VCI, with 3 equiv of Na(silox) in THF yielded (silox),M(THF) (M = Sc (ITHF), V (CTHF)), and exposure of [(Me,Si),N],Sc to 5 equiv of (silox)H provided (silox),ScNH, (3-NH,), but the bases could not be removed. Addition of C2H4, C2H,Me, I-butene, and cis-2-butene to 1 afforded (silox),Ta(olefin) (olefin = C2H4 (Sa), C2H,Me (Sb), C2H,Et (Sc), cis-MeHC=CHMe (%I)), although cyclometalation to give (~ilox)~HTa0Si'Bu~CMe~CH~ (6) competed with the latter two. In concentrated benzene solution (-0.10 M), 1 trapped C6H6 to yield [(siIo~),Ta]~[p-$( 1,2):q2(4,5)-C6H6} (7; -7%) along with 6. Acetylene, 2-butyne, and F3CC*CF3 reacted with 1 to give (silox),Ta(alkyne)...

For the first time commercially relevant catalysts for the copolymerization of ethylene and styrene have been identified. The catalysts maintain very high copolymer efficiencies at relatively high reactor temperatures without sacrificing styrene comonomer reactivity. The observations which led to this discovery are based upon the kinetic analysis of ethylene-styrene copolymerization using constrained geometry catalyst (eta5-C5Me4)(SiMe2-N-t-Bu)TiMe2 (1). This analysis revealed a substantial styrene penultimate monomer effect. Inherent reactivity of 1 toward styrene is greatly improved when the penultimate monomer on the growing polymer chain is styrene rather than ethylene. The presence of a penultimate styrene effect led to the hypothesis that catalysts bearing aromatic moieties in close proximity to the active site could lead to enhancement of styrene reactivity for this catalyst family. This hypothesis was born out by two new constrained geometry catalysts, one having two phenyl substituents placed in the 3 and 3' positions of the Cp ring (2) and the other with a 2,2'-biphenyl fragment attached to the Cp ring (3). Both catalysts exhibit higher activity than that of 1 and, more importantly, much higher styrene reactivity leading to copolymers with substantially increased styrene content (21.5% for 2, 30.6% for 3) as compared to 1 (11%) under the same polymerization conditions. Analysis of the X-ray crystal structures of 2 and 3 shows no overriding structural arguments for the increased performance. Outstanding polymerization characteristics achieved with 3 make this catalyst a candidate for commercial production of ethylene-styrene resins in a solution process.

No abstract