Inhibition of the [2 + 2 + 2] Cyclization by the Formation of Chelates: Alkyne and Vinylidene Complexes with Cyclopentadienylcobalt(I)

Abstract

The trimerization of alkynes to arenes usually observed in the reaction of cyclopentadienyl‐cobalt(I) complexes with alkynes could be prevented by chelation of the metal center with a “phosphane arm” on the cyclopentadienyl ligand. Instead alkyne complexes were obtained in very good yields. The reaction with ethyne leads to the vinylidene complex 1 (88 % yield), a possible precursor to the carbene–cobalt complex.

The First Cyclopentadienylalkylphosphane Nickel Chelates: Synthesis, Structures, and Reactions

“…As in similar cobalt complexes,2–4, 10, 11, 23, 44, 45, 50 the ethylene bridge C6C7 adopts a staggered conformation. The bond between the nickel atom and the methyl group (NiC16) is in the range of other cyclopentadienylmethylnickel complexes 51…”

Metal-Assisted Cycloaddition Reactions in Organotransition Metal Chemistry

“…Using stoichiometric amounts of [CpCoL 2 ] (L ) CO, C 2 H 2 ), the 5,6-double bond of uracil was used as olefin component and cocyclized with R,ω-diynes to give 5,6-dihydropyrimidine-2,4-diones such as 524, or 525, with one external alkyne RCtCR, and one terminal alkyne tethered to uracil-N(1). When a strongly coordinating phosphorus donor atom, as in 526 is tethered to the Cp ring, the [2+2+2] sequence is blocked, 841 and alkyne and vinylidene complexes are formed. Instead of an alkene double bond, also a CdO double bond can be utilized, and (Cp)Co complexes of R-pyrans have been obtained by Gleiter et al 842 844 with potassium naphthalenide gives the reactive anionic η 4 -benzene intermediate 529 which in situ reacts with 2 equiv of diphenylketene in [2+2+2] fashion to give the dihydroisochroman-2-one complex 530 from which the organic ligand is released by simple oxidation (eq 139).…”

The First Late‐Transition‐Metal Cyclopentadienyl Chelate Complexes with Silylphosphane or Secondary Phosphane Tethers

“…The respective ligand system is generated by nucleophilic opening of spiro[2.4]hepta-4,6diene with lithium tert-butylphosphide. Cyclopentadienyl chelate complexes with anionic tethers.In the context of our interest in cyclopentadienylalkylphosphane chelates of late-transition-metals such as cobalt [17][18][19][20][21][22][23][24][25][26][27][28][29] and nickel, [11,13] we noticed that phosphido chelates such as 9 are comparatively rare and known only for early-transition-metals such as group 4 metals, [15,[30][31][32][33] lanthanides, [34] or niobium. Treatment of lithium tert-butylphosphide with tert-butylchlorodimethylsilane or with chlorotriisopropylsilane affords the respective secondary silylphosphanes.…”