Multiple insertion and carbon-carbon coupling of isocyanides. Reaction of bis(.eta.5-methylcyclopentadienyl)zirconium dihydride with isocyanides

Synthesis and Reactivity of Cationic Group 4 Tropocoronand Complexes

“…4 The acute M-CH 16 The lack of a strong interaction between the ipso carbon and the metal is also evident in the 1 H NMR spectra of 1a and 1b, which do not display the significant upfield shift of the ortho proton resonance characteristic of η 2 -coordination of benzyl ligands. 4,8 Although the interaction with the ipso carbon atom is not strong, the acute angle at C (21) and the downfield shift of the C(21) resonance in the 13 C NMR spectrum, from δ 72.18 in [M(TC-3,3)(CH 2 Ph) 2 ] to 76.31 in 1b, are consistent with increased in Lewis acidity at the metal center following removal of one of the alkyl substituents. As was the case for the neutral [M(TC-n,m)Y 2 ] and related metallocene complexes, 13 the spectral and structural (longer M-Y bonds) results demonstrate that 1a and 1b are significantly less electrophilic compared to cationic zirconocene analogues, and the difference is especially apparent in the absence of a stabilizing ligand such as THF.…”

“…After binding to the metal center, isocyanides typically insert into the M−R bonds in organometallic group 4 complexes containing ligands such as cyclopentadienyl, aryloxide, and tetraazamacrocycles including tropocoronands. , The nitrogen atom of the isocyanide then rapidly coordinates, forming an η 2 -iminoacyl complex. Normally, in these systems, additional extrinsic substrates either bind directly to the metal center or insert, in a 1,1- or 1,2-fashion, into the M−C bond of the η 2 -iminoacyl moiety. , With 1a and 1b , however, the electrophilic nature of the bound carbon atom promotes nucleophilic attack by an additional equivalent of isocyanide, forming the ketenimine complexes 2a and 2b . The carbon atoms of η 2 -iminoacyl groups in a few zirconocene systems having constrained metallacycles are also susceptible to such direct nucleophilic attack by external isocyanides, but unlike the reactions of 2a and 2b , pressures of up to 12 kbar are required to induce this reversible conversion .…”

“…Normally, in these systems, additional extrinsic substrates either bind directly to the metal center 20 or insert, in a 1,1-or 1,2-fashion, into the M-C bond of the η 2 -iminoacyl moiety. 21,22 With 1a and 1b, however, the electrophilic nature of the bound carbon atom promotes nucleophilic attack by an additional equivalent of isocyanide, forming the ketenimine complexes 2a and 2b. The carbon atoms of η 2 -iminoacyl groups in a few zirconocene systems having constrained metallacycles are also susceptible to such direct nucleophilic attack by external isocyanides, but unlike the reactions of 2a and 2b, pressures of up to 12 kbar are required to induce this reversible conversion.…”

Double Isocyanide Insertion and C,C-Coupling Reaction of [(C5Me4)SiMe2(N-t-Bu)]ZrMe2. Structural Characterization of the Two 1,4-Diaza-5-zirconacyclopentene Ring Conformations for [(C5Me4)SiMe2(N-t-Bu)]Zr[N(R)C(Me)C(Me)N(R)] Complexes

“…The observed differences in these two C,C-coupling pathways are primarily a consequence of the level of coordinative unsaturation at the early transition metal center in the 12-electron bis(aryloxide) complexes, M(OAr) 2 R‘ 2 , and in the 16-electron (C 5 R 5 ) 2 Zr(alkyl) 2 and The presence of only one vacant metal orbital in these 16-electron complexes led us to hypothesize that a prerequisite for the direct coupling of two iminoacyl fragments is the availability of a minimum of two vacant orbitals at the electrophilic d 0 group 4 metal center …”

A Critical Review of Electronic Effects in Enediamido and α‐Diimino Complexes of the Group 4 Metals

“…As underlined before, DAD behaves as the equivalent of a six-electron donor by exploiting a filled combination of the N pπ orbitals for the third σ-type donation. [30] WEVVUO [31] WEVWAV [31] YADBEL [32] YADBIP [32] [CpTi(DAD)(NR 2 )] WORGIT [33] YAJCIV [34] [CpЈZr(DAD)(NR 2 )] NETZAN [35] NETZER [35] [Cp*Ti(DAD)(CN)] FAFMIJ [36] CpMR [Cp*Ti(DAD)(CH 3 )] ICEGUS [37] [CpTi(DAD)(CH 2 Ph)] QULSAR [38] CpML 2 [CpЈZr(DAD)(allyl)] POWVEC [39] [CpZr(DAD)(acetylacetoneiminato)] QULRIY [38] [Cp*Hf(DAD)Cl(L)] (L = imino YADYEH [40] group) [CpЈZr(DAD)(NR 2 )(NHR 2 )] WOJLAI [29] [42] JOFCIQ [43] [CpЈ 2 Zr(DAD)] FATBAD [44] HISWIP [45] JOYXIE [46] SINCAT [47] VIZWEG [48] VIZWIK [48] BAMQUC [49] [Cp 2 Hf(DAD)] QULRUK [38] [a] Cp* = C Two of the complexes in Table 3 are exceptional in that they contain a planar M(DAD) metallacycle. Their simplified formulae are [CpЈZr(NR 2 )(NHR 2 )(DAD)] and [CpЈZrCl(NHR 2 ) 2 (DAD)] (see Figure 6) and refer to the species WOJLAI and WOJLEM, [29] respectively.…”