New chemistry of 1,2-closo-P2B10H10 and 1,2-closo-As2B10H10; in silico and gas electron diffraction structures, and new metalladiphospha- and metalladiarsaboranes

Abstract

The molecular structures of 1,2-closo-P(2)B(10)H(10) (1) and 1,2-closo-As(2)B(10)H(10) (2) have been determined by gas electron diffraction and the results obtained compared with those from computation at the MP2/6-31G** level of theory. The level of agreement is good for 2 (root-mean-square [rms] misfit for As and B atoms 0.0297 Å) and very good for 1 (rms misfit for P and B atoms 0.0082 Å). In comparing the structures of 1 and 2 with that of 1,2-closo-C(2)B(10)H(12) (I) it is evident that expansion of the polyhedron from I to 1 to 2 is restricted only to the heteroatom vertices and the B(6) face to which these are bound. Following deboronation (at B3) and subsequent metallation, compounds 1 and 2 have been converted into the new metalladiheteroboranes 3-(η-C(9)H(7))-3,1,2-closo-CoAs(2)B(9)H(9) (4), 3-(η-C(10)H(14))-3,1,2-closo-RuAs(2)B(9)H(9) (5), 3-(η-C(5)H(5))-3,1,2-closo-CoP(2)B(9)H(9) (6), 3-(η-C(9)H(7))-3,1,2-closo-CoP(2)B(9)H(9) (7) and 3-(η-C(10)H(14))-3,1,2-closo-RuP(2)B(9)H(9) (8), the last three constituting the first examples of metalladiphosphaboranes. Together with the known compound 3-(η-C(5)H(5))-3,1,2-closo-CoAs(2)B(9)H(9) (3), compounds 4-8 have been analysed by NMR spectroscopy and (except for 8) single-crystal X-ray diffraction. The (11)B NMR spectra of analogous pairs of metalladiphosphaborane and metalladiarsaborane (6 and 3, 7 and 4, 8 and 5) reveal a consistently narrower (9-10 ppm) chemical shift range for the metalladiarsaboranes, the combined result of a deshielding of the lowest frequency resonance (B6) and an increased shielding of the highest frequency resonance (B8) via an antipodal effect. In crystallographic studies, compounds 3 and 5B (one of two crystallographically-independent molecules) suffer As/B disorder, but in both cases it was possible to refine distinct, ordered, components of the disorder, the first time this has been reported for metalladiarsaboranes. Moreover, whilst the Cp compounds 6 and 3 are disordered, their indenyl analogues 7 and 4 are either ordered or significantly less disordered, a consequence of both the reduced symmetry of an indenyl ligand compared to a Cp ligand and the preference of the former for a distinct conformation relative to the cage heteroatoms. Unexpectedly, whilst this conformation in the cobaltadiphosphaborane 7 is cis-staggered (similar to that previously established for the analogous cobaltadicarborane), in the cobaltadiarsaborane 4 the conformation is close to cis-eclipsed.

The presence of cobaltdibismuth triangular faces in the lowest energy deltahedral cobaltadibismaborane polyhedra: Major differences from their cobaltadiphosphaborane analogues

“…In all of the lowest energy CpCoP 2 B nÀ3 H ne3 structures the central CoP 2 B ne3 polyhedra are found to be the most spherical deltahedra similar to those found in the corresponding B n H 2À n dianions ( Fig. 1 for n ¼ 10, 11,12). The lowest energy CpCoP 2 B nÀ3 H ne3 structures typically but not always have the cobalt atom at a degree 5 or 6 vertex and the phosphorus atoms at degree 4 vertices.…”

“…Major differences between the preferred structures of the cobaltadiphosphaboranes CpCoP 2 B ne3 H ne3 and those of the corresponding cobaltadibismaboranes CpCoBi 2 B nÀ3 H ne3 (n ¼ 10, 11,12) are predicted from this theoretical study. In particular, the lowest energy CpCoP 2 B ne3 H ne3 structures were previously found to have the phosphorus atoms as far apart as possible [14].…”

“…In this connection replacement of two CH groups by bare phosphorus atoms in the dicarbaboranes C 2 B nÀ2 H n gives the corresponding diphosphaboranes P 2 B ne2 H ne2 . The icosahedral diphosphaborane P 2 B 10 H 10 was first synthesized in relatively low yield by Todd and co-workers in 1989 [11] and much later in better yield by Welch and co-workers [12]. An isomer of the cobalt complex CpCoP 2 B 9 H 9 has been synthesized from P 2 B 10 H 10 and structurally characterized by X-ray crystallography [13].…”

Phosphorus as a heteroatom in metallaborane structures: Cyclopentadienylcobalt diphosphaboranes

“…Recently the syntheses of the icosahedral cobaltadiphosphaborane CpCoP 2 B 9 H 9 and its indenyl analog (g 5 -C 9 H 7 )CoP 2 B 9 H 9 were reported [11]. X-ray crystallography showed these products to have the structure B9P2Co-6 with a CoP 2 triangular face rather than the lowest energy structure B9P2Co-1 ( Fig.…”

“…The isomerization of P 2 B 10 H 10 upon pyrolysis is completely analogous to that of the dicarbaborane C 2 B 10 H 12 . Recent modifications of the synthesis of P 2 B 10 H 10 have led to a significant improvement in the yield and thus its availability for the synthesis of metal complexes [11]. An isomer of the cobalt complex CpCoP 2 B 9 H 9 has been synthesized from P 2 B 10 H 10 and structurally characterized by X-ray crystallography (Fig.…”