Ligand exchange in TaX(.eta.4-naphthalene)(Me2PC2H4PMe2)2. The pentagonal bipyramid to monocapped trigonal prism traverse

From Storable Sources of Atomic Nb− and Ta− Ions to Isolable Anionic Tris(1,3‐butadiene)metal Complexes: [M(η4‐C4H6)3]−, M=Nb, Ta

“…[14,19] All other data for 3, and the tantalum complex, indicate the presence of substantial metal-naphthalene back-bonding. [20,21] Undoubtedly the most exciting reaction of 3 discovered to date, and one which establishes its utility as a storable source of naked Nb À ions, is that with excess 1,3-butadiene, which affords the tris(butadiene)metal complex [Nb(h 4 [24]…”

“…[19] Generally, complexes of this type have MÀC(diene) bonds that show a short-long-long-short pattern. [15] However, the pattern may be weak, as in the case of 1, [5] or even inverted, as in the case of 3 and [TaCl(h 4 -C 10 H 8 )(dmpe) 2 ], [14] because the outer MÀ C(diene) bonds are elongated by bulky substituents on the dienes, for example, the exo-benzene group on h 4 -naphthalene, and/or on the metal center, for example, organophosphane groups. For example, the average outer MÀC1/C4 and inner MÀ C2/C3 bond lengths in 3 are 2.40(1) and 2.282(6), whereas the corresponding values for Wrefords tantalum naphthalene complex are 2.39(3) and 2.25(1) , respectively.…”

From Storable Sources of Atomic Nb− and Ta− Ions to Isolable Anionic Tris(1,3‐butadiene)metal Complexes: [M(η4‐C4H6)3]−, M=Nb, Ta

“…Interatomic distances associated with the niobium-h 4 -diene units in 3 show a normal long-short-long pattern in the C À C bonds, similar to that in 1, [18] and characteristic of strong metal to diene backbonding. [14,19] All other data for 3, and the tantalum complex, indicate the presence of substantial metal-naphthalene back-bonding. [14,19] All other data for 3, and the tantalum complex, indicate the presence of substantial metal-naphthalene back-bonding.…”

“…From this reaction mixture, the satisfactorily pure anion [Nb(h 4 -C 10 2 ] À , and is a precursor to an unprecedented niobium-butadiene complex (see below). It is also the first niobium-naphthalene complex to be described, which is surprising because numerous other niobium arenes have been reported [12] and several vanadium- [3,13] and tantalum-naphthalene [5,14] complexes are well-established. However, none of these prior complexes are analogous to 3.…”

“…[15] The corresponding NbÀC(diene) bonds have a definite long-short-short-long pattern, which is unusual among early-transition-metal-diene complexes, [15,19] but well-precedented in Wrefords crowded Ta I -naphthalene complex [TaCl(h 4 -C 10 H 8 )(dmpe) 2 ] (dmpe = 1,2-bis(dimethylphosphano)ethane). [14,19] All other data for 3, and the tantalum complex, indicate the presence of substantial metal-naphthalene back-bonding. [20,21] Undoubtedly the most exciting reaction of 3 discovered to date, and one which establishes its utility as a storable source of naked Nb À ions, is that with excess 1,3-butadiene, which affords the tris(butadiene)metal complex [Nb(h 4 -C 4 H 6 ) 3 ] À (4).…”