Synthesis, structural characterization, and reactivity of late transition-metal complexes bearing linked cyclopentadienyl–carboranyl ligands

Abstract

Late transition-metal complexes bearing linked cyclopentadienyl/indenyl-carboranyl ligands were synthesized and their reactivities were examined. Reaction of Li2[Me2C(L)(C2B10H10)] (L = C5H4, C9H6, Me2NCH2CH2C5H3) with MCl2(PPh3)2 in Et2O afforded [h 5 :s-Me2C(C5H4)(C2B10H10)]M(PPh3) (M = Co (4), Ni (5)), [h 5 :s-Me2C(C9H6)(C2B10H10)]M(PPh3) (M = Co (6), Ni (7)), and [h 5 :s-Me2C(Me2NCH2CH2C5H3)(C2B10H10)]Ni(PPh3) (8). Treatment of 4 or 5 with 2,6-dimethylphenylisocyanide, N-heterocyclic carbene (NHC), PCy3, or 1,2-bis(diphenylphosphino)ethane (dppe) gave the corresponding PPh3 displacement complexes [h 5 :s-Me2C(C5H4)(C2B10H10)]M(2,6-Me2C6H3NC) (M = Co (9), Ni (10)), [h 5 :s-Me2C(C5H4)(C2B10H10)]M[1,3-(2,6-i-Pr2C6H3)2C3N2H2] (M = Co (11), Ni (12)), [h 5 :s-Me2C(C5H4)(C2B10H10)]Ni(PCy3) (13), or {[h 5 :s-Me2C(C5H4)(C2B10H10)]Co}2(dppe) (14), respectively. These complexes were characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 4-14 were further confirmed by singlecrystal X-ray analyses.

Reactivity of Traditional Metal–Carbon (Alkyl) versus Nontraditional Metal–Carbon (Cage) Bonds in Organo-Rare-Earth Metal Complexes [η5:σ-(C9H6)(C2B10H10)]Ln(CH2C6H4-o-NMe2)(THF)2

“…These results show that unsaturated molecules can insert into the Ln–C alkyl σ bond to give the monoinsertion products, suggesting that the Ln–C alkyl bond is more reactive than the Ln–C cage one. Such results are consistent with our earlier observations in the reaction chemistry of metal–carboranyl complexes. , …”

“…Our previous work has shown that the M–C cage bonds in transition-metal–carboranyl complexes are generally inert toward electrophiles and, hence, significantly different from traditional M–C bonds. This lack of reactivity can be ascribed to steric effect imposed by the carboranyl moiety. , To overcome such steric problem and to activate M–C cage bonds, a series of metal–carboryne complexes bearing a three-membered metallacyclopropane ring are prepared since a more open coordination sphere around the metal and ring strain can enhance the reactivity of M–C cage bonds …”

N-Heterocyclic Carbene Complexes of Copper, Nickel, and Cobalt

“…The NHC amidinato complex 32 Co (Scheme 281) was formed by aminolysis of the Co−N(SiMe 3 ) 2 bond in 27a sCo upon reaction with N,N′-bis(cyclohexyl)acetamidine. 572 The Co II center is η 5 -bound to the Cp ring, σ-bound to the cage carbon atom, and further coordinated to the NHC ligand. 16).…”

“…With the use of a linked cyclopentadienyl-carboranyl [η 5 :σ-Me 2 C­(C 5 H 5 )­(C 2 B 10 H 10 )] ligand, the NHC complex 48 Co was obtained by substitution of the phosphine ligand in [Co­{η 5 :σ-Me 2 C­(C 5 H 5 )­(C 2 B 10 H 10 )}­(PPh 3 )] (Scheme ). The Co II center is η 5 -bound to the Cp ring, σ-bound to the cage carbon atom, and further coordinated to the NHC ligand.…”

Tethered N-heterocyclic carbene–carboranes: unique ligands that exhibit unprecedented and versatile coordination modes at rhodium

“…Ortho-carborane precursors can be easily modified by substituting the acidic cage hydrogen atom(s) at the cluster carbons with groups that have desirable electronic and steric effects. This includes the addition of tethering substituents such as amino [11][12][13] or cyclopentadienyl [14][15][16] groups. Herein, we report unprecedented tethered NHC-carborane ligands ( Fig.…”