Methyl Displacements from Cyclopentadienyl Ring Planes in Sterically Crowded (C₅Me₅)₃M Complexes

Abstract

The displacements of the methyl substituents away from the metal and out of the cyclopentadienyl ring plane are compared in sterically crowded (C(5)Me(5))(3)M complexes vs sterically normal f-element complexes in an attempt to evaluate the utility of this parameter in predicting unusual (C(5)Me(5))(1-) ring reactivity. The out-of-plane displacements of 16 sterically crowded tris(cyclopentadienyl) complexes of general formula (C(5)Me(5))(3)M, (C(5)Me(4)R)(3)M (R = Et, (i)Pr, (t)()Bu, SiMe(3)), (C(5)Me(5))(3)MX (X = anion), and (C(5)Me(5))(3)ML (L = neutral ligand) are compared with [(C(5)Me(5))(2)U](2)(C(6)H(6)), (C(5)Me(5))(2)Sm(PC(4)H(2)(t)Bu(2)), and 33 representative examples of f-element bis(cyclopentadienyl) complexes with normal cyclopentadienyl behavior and coordination numbers ranging from 6 to 10. In general, the methyl displacement values of sterically crowded complexes overlap with those in the other complexes, which demonstrates that the basis of the structural distortions is complex. However, if the most extreme out-of-plane displacement in each of the sterically crowded complexes is examined vs the analogous maximum out-of-plane displacement in less crowded systems, there appears to be a basis for predicting cyclopentadienyl reactivity.

C–H bond activation through steric crowding of normally inert ligands in the sterically crowded gadolinium and yttrium (C 5 Me 5 ) 3 M complexes

“…Recently, an analysis of the bending of the methyl groups out of the plane of the cyclopentadienyl ring in sterically crowded (C 5 Me 5 ) 3 M complexes was published (29). This analysis shows that, although there is a large range in the out-of-plane displacement distances for the methyl groups in any specific complex, the most extreme value, the largest out-of-plane displacement, is the most diagnostic for unusual (C 5 Reactivity.…”

Advances in f element reductive reactivity as a paradigm for expanding lanthanide and actinide science and technology

“…The 2.82 (5) Å average was larger than the typical averages, 2.71 (2)-2.75 (2) Å [75], and the three crystallographically independent Sm-C(C 5 Me 5 ) distances displayed the larger than normal values of 2.782 (2), 2.817 (2), and 2.910 (3) Å. Bending the methyl substituents back out of the plane of the (C 5 Me 5 ) 1− ring would also reduce the cone angle. Subsequent analyses have shown that this is a complicated situation in these long bond organometallics in which only one of the three crystallographically unique methyl groups has unusual bending out of the plane [76].…”

Two-electron reductive reactivity of trivalent uranium tetraphenylborate complexes of (C5Me5)1− and (C5Me4H)1−

“…Specifically, (C 5 Me 5 ) 1À can become a one-electron reductant in sterically crowded complexes such as (C 5 Me 5 ) 3 U [5] and [(C 5 Me 5 ) 2 U] 2 (C 6 H 6 ) [2] in which the U-C(C 5 Me 5 ) distances are unusually long [6]. By combining this ligand-based reduction with the reducing U 3+ ion, these complexes become capable of multi-electron reduction as shown in the four-electron reduction in Scheme 1 [3].…”

“…Accordingly, the reductive reactivity of the tetramethylcyclopentadienyl complex [(C 5 Me 4 H) 2 U][(l-g 6 :g 1 -Ph)(l-g 1 :g 1 -Ph)BPh 2 ] (2) [9] was examined. Complex 2 differs from 1 in that one phenyl group is oriented g 6 to U 3+ and the other is g 1 , whereas 1 has two g 2 -phenyl groups. We report here a comparison of (BPh 4 ) 1À reduction chemistry with 1 and 2.…”