Reactions of Decamethylhafnocene with 1,3-Butadiynes: Formation of Hafnacyclocumulenes and C−H Activation at Pentamethylcyclopentadienyl Ligands

Abstract

The reduction of Cp*2HfCl2 with lithium in the presence of disubstituted butadiynes RCC−CCR (R = Ph, SiMe3, t-Bu) in toluene leads, respectively, to the five-membered hafnacyclocumulene complexes Cp*2Hf(η4-1,2,3,4-PhC4Ph) (1-Hf) and Cp*2Hf(η4-1,2,3,4-Me3SiC4SiMe3) (2-Hf) and, in the case of 1,4-bis(tert-butyl)butadiyne by a 2-fold activation of the methyl groups of one pentamethylcyclopentadienyl ligand, to the complex Cp*Hf[−C(CCH-t-Bu)−CH(t-Bu)CH2−η5-C5Me3−CH2−] (3-Hf) containing a fulvene ligand that is coupled to the modified substrate (allenic subunit). The latter inserts 2 equiv of the isocyanide t-BuNC to give by coupling of the isocyanide molecules the complex Cp*Hf[−C(CCH-t-Bu)−CH(t-Bu)CH2−η5-C5Me3−CH2−C(N-t-Bu)−C(N-t-Bu)−] (4). The structures of complexes 3-Hf and 4 were determined by X-ray crystallography.

Multiple and Highly Selective Alkyne–Isonitrile C−C and C−N Couplings at Group 4 Metallocenes

“…The 13 C NMR resonances of the coordinated carbon atom (C2) appear at low field ( 5 a : 171.0, 5 b : 172.1, 5 c : 175.6 ppm) and are in accordance with those previously reported for a zirconocene η 2 ‐(C,N)‐enimine complex (170.3 ppm) . Besides a titanocene fulvene complex further examples of metallocene complexes with such a η 2 ‐(C,N)‐bonded (C=C=N) unit were also reported for Nb, V and Fe –…”

“…1 H NMR spectroscopy of 3 revealed that both isocyanide ligands are equivalent, giving only one signal ( δ =2.26 ppm) for the methyl groups at the aromatic ring besides one set of signals for the rac ‐(ebthi) ligand and for the xylyl protons. The 13 C NMR resonance of the isocyanide group ( δ =248.2 ppm) is in the expected range for titanium compounds with end‐on bonded isocyanide groups . The corresponding Cp‐substituted complex [Cp 2 Ti(η 1 ‐CNXy) 2 ] shows a broadening of the signals at ambient temperature, which is not observed for 3 .…”

“…The C−N bond distances (C1−N1 and C10−N2) are in the same range and correspond to a slightly elongated C(sp)≡N(sp) triple bond, but both isocyanide fragments display a significant deviation from the linearity of the C‐N‐C Xy unit [C1‐N1‐C2 154.14(12), C10‐N2‐C11 155.24(12)°]. This observation was reported before for the complex [Cp* 2 Ti(η 1 ‐CN‐Mes) 2 ], which displays two inequivalent isocyanide groups in the solid state [C‐N‐C Mes 142.4(2)/176.1(2)°; Mes=2,4,6‐trimethylphenyl) . A possible explanation was given by Filippou et al., who reported that a very strong back donation from the metallocene fragment to the isocyanide ligand induced the bending .…”

Crystal structure of bis(pentamethylcyclopentadienyl)(1-tert-butylisocyanido)-2-trimethylsilyl-3-[(trimethylsilyl)ethynyl]-hafnacyclopropene, (C10H15)2(C5H9N)Hf(C10H18Si2)

“…Recently we have reported on the interactions of 1,3-butadiynes with permethylhafnocene, resulting in the formation of fivemembered hafnacyclocumulenes [1]. We were interested to investigate the reaction behaviour of these complexes especially with respect to insertion reactions, e.g.…”

Reactivity of Tuck-over Titanium Oxo Complexes with Isocyanides

“…The first crystallographically characterized tuck-over derivative in the literature, [Ti 2 (η 5 -C 5 Me 5 ) 2 ­(μ-η 5 -C 5 Me 4 ­CH 2 -κ C )­(μ-O) 2 ], was obtained by the reaction of N 2 O and a toluene solution of [Ti­(η 5 -C 5 Me 5 ) 2 ] . In contrast to the tuck-in analogous, which exhibited interesting reactivity, − Bottomley’s showed a remarkable inertness toward O 2 , CO, ethylene, or even H 2 . Later, Evans reported the crystal structure of [(η 5 -C 5 Me 5 ) 2 ­Lu­(μ-H)­(μ-η 5 -C 5 Me 4 ­CH 2 -κ C )­Lu­(η 5 -C 5 Me 5 )], a tuck-over complex of an f-block element.…”