The photochemical decarbonylation and rearrangement of the small phosphorus-bridged, σ-metalated pentaborane(9) cluster [Fe(η5-C5H5)(CO)2B5H7(μ-P(C6H5)2)] (3) was found to produce the organometallic tetraborane cluster complex [Fe(η5-C5H5)(CO)B4H6(P(C6H5)2)] (4). The conversion of 3 to 4 was found to be accompanied by the loss of a carbonyl ligand from the iron fragment, the loss of a boron vertex from the cage, and a structural rearrangement to yield the new complex. The structure of complex 4 is based on a substituted arachno-pentaborane(11) parent cluster in which one of the BH2 basal boron atoms has been replaced by an Fe(η5-C5H5) (CO) (μ-PPh2) fragment and a terminal endo-hydrogen on the opposite basal boron has been replaced by a diphenylphosphino group. The phosphine is also σ-bound to the iron center in a B-P-Fe bridged mode. Complex 4 was readily converted into the triborane complex [Fe(η5-C5H5)(CO)B3H7(P(C6H5)2)] (5) through the loss of an additional vertex boron atom by passing 4 down a silica gel column. Both complexes 4 and 5 are relatively air stable materials. A single-crystal X-ray analysis of 5 shows that the structure is based on a substituted arachno-B4H10 structure. An alternate description for 5 is based on a metalated B3H8− structure in which the iron fragment coordinates to one boron atom of the B3H8− ligand through a M-H-B interaction and the phosphorus atom bridges between the iron and the adjacent boron atom in much the same fashion as a bridging M-H-B hydrogen atom. Complex 5 represents the first structurally characterized metal triborane complex which exhibits a 1103 styx structure. The complete characterization by 1H, 11B, 13C, 31P NMR, infrared, and mass spectral analyses is reported. Crystallographic data for 5: space group P21/c (No. 14), a = 8.506 (1) Å, b = 14.127 (3) Å, c = 16.121 (3) Å, α = γ = 90.00°, β = 102.73 (1)°, V= 1889.5 (6) Å3, Z = 4 molecules/cell.
ASJC Scopus subject areas
- Colloid and Surface Chemistry