Studies with the Rhenacarborane Cs[Re(CO)₃(η⁵-7,8-C₂B₉H₁₁)]:  Surprising Reactivity with a Range of Metal Ligand Fragments

Abstract

The rhenacarborane salt Cs[Re(CO) 3 ( η 5 -7,8-C 2 B 9 H 11 )] ( 1 ) has been synthesized in excellent yield using a new procedure. Treatment of CH 2 Cl 2 solutions of 1 with [RuCl 2 (PPh 3 ) 3 ] yields the exo - closo complex [Re(CO) 3 ( η 5 -2,3,10-( μ -H) 3 - exo -{RuCl(PPh 3 ) 2 }-7,8-C 2 B 9 H 8 )] ( 2a ). In this molecule a [RuCl(PPh 3 ) 2 ] + moiety is exopolyhedrally bound via three B−H⇀Ru bonds to a closo -3,1,2-ReC 2 B 9 system. An X-ray diffraction study revealed that one of these agostic interactions utilizes a β -B−H bond in the coordinating face of the cage, while the source of the remaining two B−H⇀Ru bonds is in the B 5 belt. The anion of salt 1 also binds exopolyhedral [Rh(PPh 3 ) 2 ] + and [Rh{Fe( η -C 5 H 4 PPh 2 ) 2 }] + fragments in the complexes [Re(CO) 3 ( η 5 -5,10-( μ -H) 2 - exo -(RhL 2 )-7,8-C 2 B 9 H 9 )] (L 2 = (PPh 3 ) 2 ( 3a ), {Fe( η -C 5 H 4 PPh 2 ) 2 } ( 3b )). Reaction of 1 with the salts [M(CO) 2 (THF)( η -C 5 H 5 )][BF 4 ] (M = Fe, Ru) and [Fe(CO) 2 (THF)( η -C 5 Me 5 )][BF 4 ] gives the complexes [Re(CO) 3 ( η 5 - n -( μ -H)- exo -{M(CO) 2 ( η -C 5 R 5 )}-7,8-C 2 B 9 H 10 )] (M = Fe, R = H, n = 10 ( 4a ); M = Ru, R = H, n = 10 ( 4b ); M = Fe, R = Me, n = 10 ( 4c ), 9 ( 4d )) with isomers 4c and 4d formed as an inseparable mixture. An X-ray structural study on 4b revealed that there was no Re−Ru bond and that an exo -[Ru(CO) 2 ( η -C 5 H 5 )] + fragment is bound to the rhenacarboranyl anion by a single unsupported B−H⇀Ru interaction with an unusually long B−Ru distance (2.695(13) Å). The compounds [ReM( μ -10-H- η 5 -7,8-C 2 B 9 H 10 )(CO) 3 (PPh 3 )] (M = Cu ( 5a ), Ag ( 5b )) were isolated from the reaction of 1 with sources of the fragments [M(PPh 3 )] + (M = Cu, Ag). X-ray structure determinations of both species 5 revealed the presence of direct Re−M (M = Cu, Ag) connectivities bridged by carborane β -B−H⇀M interactions. In solution the complexes 5 are highly dynamic on the NMR time scale, even at low (−90 °C) temperatures.