Dimethylallenediyl as an η¹,η²-bridging ligand in a dizirconocene complex

Abstract

Treatment of (q2-ethene)(trimethylphosphane)zirconocene 1 with 3,3-dimethylcyclopropene 2 leads to the formation of a new type of bis(ethy1zirconocene) complex 3 with 3,3-dimethylallenediyl as a yl,p2-bridging ligand; the crystal structure of 3 is determined by X-ray analysis.

Transition Metal Complexes Containing Allenylidene, Cumulenylidene, and Related Ligands

“…However, the NMR spectrum indicates rapid fluxionality at room temperature, with only slight broadening of the CH 2 signals at −80 °C. The proposed process (Scheme ) involves a symmetrical μ-allenediyl (allenylidene) intermediate 56 …”

“…The proposed process (Scheme 56) involves a symmetrical µ-allenediyl (allenylidene) intermediate. 195…”

A Bridging Side-on Allenylidene Dimolybdenum Complex without Carbonyl Stabilization

“…The length of the Mo−Mo single bond in 4 (2.659(9) Å) is close to the average value for [Mo 2 III (μ-SR) 3 ] complexes (2.644 Å), and the μ-Mo−S distances are also unexceptional . The short Mo2−C4 distance (1.88(1) Å) formally represents a double bond; comparable distances are found in related neutral side-on allenylidene derivatives, such as [Mo 2 Cp 2 (CO) 4 (μ-η 1 :η 2 -CCCMe 2 )] (1.912(3) Å) 5f and [Mo 2 Cp 2 (CO) 4 (μ-η 1 :η 2 -CCC 6 H 10 )] (1.90(1) Å),5d formally Mo(I) species, and in the cationic vinylidene derivative [Mo 2 Cp 2 (μ-SMe) 3 (μ-η 1 :η 2 CCPh 2 )](BF 4 ) (1.894(5) Å) 10a. In comparison to μ-η 1 :η 1 (2e) allenylidene ligands, which are linear, the C 3 Ph 2 fragment in 4 is kinked, with C4−C5−C6 = 144.0(1)°.…”

“…This is in accord with the observed line broadening of the Cp resonance when a dichloromethane- d 2 solution of 4 is cooled from 298 to 174 K. The 13 C{ 1 H} NMR spectrum contains a resonance at low field (δ 302.0) assignable to a carbenoid carbon atom (C α ). This low-field chemical shift is indicative of an asymmetric side-on coordination mode of the allenylidene group bridging a bimetallic core ([M]−[M]), for which a 13 C α chemical shift range of 302−282 ppm has been observed in known μ-allenylidene (side-on) dinuclear derivatives, 5b,d,f and it is in contrast with the values of 206.5−173 ppm reported for related end-on species. 5a,c,e In short, these spectroscopic data suggest that 4 has a highly unsymmetrical structure in solution. Single-crystal X-ray analysis confirms that the cation of 4 displays the unsymmetrical side-on coordination of the allenylidene group (Figure ), bridging the metal−metal bond as a four-electron donor.…”

“…The vast majority of known allenylidene complexes are mononuclear . General methods of synthesis for binuclear or polynuclear derivatives are unavailable, and consequently, there have been only a few reports of such complexes. , Two well-established bridging modes have been found for allenylidenes in binuclear complexes, the μ-η 1 :η 1 (2e) (end - on) 5a,c,e,g-i and μ-η 1 :η 2 (4e) (side-on) 5b,d,f forms; however, there are also examples of dinuclear complexes containing nonbridging allenylidene ligands (2e). 3a, All known dinuclear and polynuclear complexes containing bridging allenylidene ligands also contain carbonyl ligands; , the only possible exception is [{Cp 2 ZrEt} 2 (μ-CCCMe 2 )], where one Zr atom appears to interact with all three chain carbon atoms 5k. Accordingly, in an attempt to synthesize μ-allenylidene complexes which do not owe their stability to the presence of carbonyl ligands, we have reacted the bis(isonitrile) compound [Mo 2 Cp 2 (μ-SMe) 3 (NCCH 3 ) 2 ](BF 4 ) ( 1 ) with propargylic alcohols, followed by sequential treatment with triethylamine and tetrafluoroboric acid.…”