Di- and tri-cobalt carbonyl clusters bearing geranyl or neryl substituents offer potential routes to novel terpenoid systems.
Treatment of methyl geranyl ether with diiron nonacarbonyl leads to hydrogen migration to form previously unknown E and Z 1-methoxy-3,7-dimethyl-1,6-octadiene in low yield. Sodium propargyl alkoxide and geranyl bromide yield propargyl geranyl ether, 13 ; subsequent reaction with dicobalt octacarbonyl and then bis(diphenylphosphino)methane furnishes the corresponding alkyne–Co 2 (CO) 4 (dppm) tetrahedral cluster, 16 . Reaction of geranylacetone with phenylethynyl-lithium, and then with Co 2 (CO) 8 , forms (1-phenyl-3,7,11-trimethyldodeca-6,10-dien-1-yn-3-ol)Co 2 (CO) 6 , 19 . The carbynyltricobaltnonacarbonyl clusters RC(O)CCo 3 (CO) 9 , where R = geranyl, 23 , or farnesyl, 25 , are preparable in very good yield either by reaction of the appropriate alcohol with trichloroacetyl chloride and then Co 2 (CO) 8 , or by reaction with the metal-stabilized acylium ion [Co 3 (CO) 9 CCO] + , 24 . Potential use of these (η 2 -alkyne)dicobalt complexes in Pauson–Khand or Nicholas cyclizations is discussed.