Synthetic and Structural Studies of Heteroatom−Polyborane Clusters:  Simple, High-Yield Syntheses of nido-11-Vertex Thia- and Phosphaboranes, Thia- and Phosphadicarbaboranes, and the First Thiaphosphaborane

Abstract

A synthetic sequence involving the reaction of a phosphorus or sulfur dihalide with a monoanionic boron cluster followed by an in situ dehydrohalogenation reaction initiated by proton sponge results in the clean insertion of the heteroatom into the cage framework. Using this method, a range of nido-11-vertex thia- and phosphaboranes, thia- and phosphadicarbaboranes, and the first thiaphosphaborane has been produced in high yields. Thus, the reaction of decaborane with SCl2 or RPCl2 and excess proton sponge gave the known anions, nido-7-SB10H11 - (1 -) and nido-7-RPB10H11 - [2a - (R = Me) and 2b - (R = Ph)], respectively. Acidification of 1 -, 2a -, and 2b - resulted in the isolation of nido-7-SB10H12 (1) and nido-7-RPB10H12 (2a and 2b), respectively, in near-quantitative yields. Reaction of nido-5,6-C2B8H12 with SCl2 or RPCl2 in the presence of proton sponge produced the new compounds, nido-7,10,11-SC2B8H10 (3) (77%) and nido-7,10,11-RPC2B8H10 [R = Me (97%) 4a, Ph (83%) 4b], respectively. Reaction of arachno-6-SB9H11 with PhPCl2 and proton sponge resulted in the formation of the new mixed heteroatom cage, nido-10-Ph-7,10-SPB9H9 (5), which is the first example of a thiaphosphaborane cluster. Consistent with their nido skeletal electron counts, all clusters were shown by spectroscopic and DFT/GIAO computational studies to have similar cage frameworks containing a five-membered open face.

Periodic trends and easy estimation of relative stabilities in 11-vertex nido-p-block-heteroboranes and -borates

“…A similar profound preference is found for the heteroatom apart nido-7,9-isomer (FA) [70] among [SCB 9 H 10 ] À structures. The experimentally known nido-7,9,10-SC 2 B 8 H 10 (GA) [3] is the most stable of the seven computed isomers. nido-7,8,9-SC 2 B 8 H 10 (GE) [3] and nido-7,8,10-SC 2 B 8 H 10 (GB) [3] with E calc =32.9 and 14.2 kcal mol À1 , respectively are also experimentally known.…”

“…The experimentally known nido-7,9,10-SC 2 B 8 H 10 (GA) [3] is the most stable of the seven computed isomers. nido-7,8,9-SC 2 B 8 H 10 (GE) [3] and nido-7,8,10-SC 2 B 8 H 10 (GB) [3] with E calc =32.9 and 14.2 kcal mol À1 , respectively are also experimentally known. 8,2,10-(GC) and 7,1,9-SC 2 B 8 H 10 (GD) are thermodynamically more stable than 7,8,9-SC 2 B 8 H 10 (GE) [3], but are still experimentally unknown.…”

“…The experimentally known [3,34,68] [69] nido-7,9-S 2 B 9 H 9 (DA) is the most stable isomer as it lacks any structural feature. None of the dithiaborane starting geometries with two adjacent sulfur atoms optimized successfully but converged to rearranged structures.…”

“…DFT computed relative energies are also reported for HA to HD. All values are in kcal mol 7-Ph-HB, i.e., 7-Ph derivative of 7,9-PSB 9 H 10 is experimentally known energy than the former and its phenyl derivative i.e., nido-7-Ph-7,9-PSB 9 H 9 was experimentally characterized [3].…”

“…Many reactions are known [1][2][3] to incorporate a hetero-fragment into a smaller nido-or arachno-cluster, leading to 11-vertex nido-heteroboranes. Removal of one vertex from a 12-vertex closo-heteroborane cluster also leads to 11-vertex nido-heteroboranes and -borates [2,4,5].…”