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)...
