Steric Influence on the Reactivity of Silyl-o-carboranes:  Oxidative-Addition Reactions Involving Si−H and B−H Activation

Abstract

The reactivity of mono(silyl)- and bis(silyl)-o-carboranes (HSiR2) n (C2B10H12 - n ) (n = 1, R = Me, 1a; n = 1, R = Et, 1b; n = 2, R = Me, 3a; n = 2, R = Et, 3b) toward six-coordinate iridium [(Cp*IrCl2)2] and nine-coordinate rhenium [ReH7(PPh3)2] complexes has been investigated. Reactions between the mono(silyl)-o-carboranes (1a,b) and (Cp*IrCl2)2 resulted in the formation of four-membered, cyclic seven-coordinate iridium complexes Cp*IrH2[η1:η1-(SiR2)BC2B9H10-Si,B] (R = Me, 2a; R = Et, 2b), where Si−H activation in the mono(silyl)-o-carborane (1) is accompanied by the concomitant B−H activation of a neighboring boron hydride. The X-ray structure of 2a reveals that the iridium center is coordinated to both silicon and boron in a four-legged piano-stool arrangement. In the reaction between the bis(silyl)-o-carboranes (3a,b) and (Cp*IrCl2)2, silylation occurs at both Si−H sites, giving rise to the complexes Cp*IrH2[η1:η1-(SiR2)2C2B10H10-Si,Si ‘] (R = Me, 4a; R = Et, 4b), in which the metal center forms part of a five-membered metallacycle (Ir−Si−C−C−Si). Interestingly, the reaction of 3a with ReH7(PPh3)2 afforded the kinetically stabilized intermediate (PPh3)2ReH5[η1-SiMe2C2B10H10(SiMe2H)-Si] (8), in which only one of the Si−H groups is coordinated, as determined by X-ray crystallography.

Versatile Reactivity of Half‐Sandwich Ir and Rh Complexes toward Carboranylamidinates and Their Derivatives: Synthesis, Structure, and Catalytic Activity for Norbornene Polymerization

“…For Ir complexes, the Ir(1) À B(3) bond lengths (2.044(10) 3 a, 2.051(13) 3 b) are similar to reported values. [21] The Ir(1)ÀN(1) bond lengths of 2.076 (7) and 2.077 (7) , respectively, are within the range of known of IrÀN bond lengths in analogous complexes. [5, 21a] The Ir(1)ÀS(1) bond lengths of 2.419(4) and 2.435(3) , respectively, are within the normal range of Ir À S bonds, [21a] but are much longer than those in 16-electron complex Cp*IrS 2 A C H T U N G T R E N N U N G [C 2 B 10 H 10 ].…”

Reactions of Hydrosilanes with Transition Metal Complexes and Characterization of the Products

“…172 In a related reaction of excess o-(HMe 2 Si)C 6 H 4 with (1/2)[Cp*IrCl 2 ] 2 , the complexes trans-Cp*(Cl)(H)Ir-[SiMe 2 C 6 H 4 SiMe 2 ] (3-230) and trans-Cp*(H) 2 Ir-[SiMe 2 C 6 H 4 SiMe 2 ] (3-231) were isolated in about a 1.5:1 ratio. 172 The Ru(II) dimer, [(pcymene)RuCl 2 ] 2 , reacted with HSiPh 3 to give the equivalent of oxidative addition to provide monometallic 3-102. 191 Hydrosilanes that contain two base tethers may function as a "tridentate".…”

“…172 90 The positions of the hydrides were determined from difference maps. 172 123 98 Hydrides located by difference Fourier map and included in structure calculations but not refined. 123 99 Average value for Pd1-SiH 2 .…”

Iridium‐Catalyzed Regioselective B(3)‐Alkenylation/B(3,6)‐Dialkenylation of o‐Carboranes by Direct B−H Activation

“…On the basis of the aforementioned experimental results and literature work, a possible mechanism for alkenylation and alkynylation reactions is proposed in Scheme . Oxidative addition of the terminal alkyne on the Ir center gives an intermediate A .…”

“…Reductive elimination leads to the formation of the iridium acetylide B . Oxidative addition of cage B(3)−H on the Ir center generates the Ir V hydride C . For alkylacetylenes, 1,3‐hydrogen migration affords a vinylidene intermediate D , followed by 1,2‐migration of the cage to the α‐carbon to afford E / E′ .…”