Reduction of carbon monoxide promoted by alkyl and hydride derivatives of permethylzirconocene

Alkaline‐Earth‐Promoted CO Homologation and Reductive Catalysis

“…(1)]. [3] These deductions were confirmed through as ubsequent X-ray structural analysis,the results of which are illustrated in Figure 1, performed on as elected single crystal of compound 1 grown from as aturated n-pentane solution. While the C30-C31 distance [1.327(3) ] is clearly indicative of the formation of aC =Cdouble bond and a cis-enediolate similar to that observed in both compounds II and III,the ligand does not display ad irectly analogous symmetrical bridging disposition.…”

“…[1] Although Fischer-Tropsch (F-T) chemistry and related processes have been successfully implemented for some eighty years to produce aS chultz-Flory distribution of hydrocarbons,o nly limited success has been achieved with well-defined homogeneous systems,t ypically at CO pressures in excess of 1000 atm. [2] More recent activity has targeted the synthesis of putative F-T intermediates including,and most pertinent to the current work, enediolates such as the zirconium and cerium species I-III,which were prepared through treatment of the relevant metal hydride with CO. [3] Our own research efforts have focused on the development of ah omogeneous catalytic chemistry for complexes derived from the inexpensive and environmentally benign alkaline-earth elements, [4] in particular magnesium and calcium;r espectively the eighth and fifth most abundant elements in the lithosphere.I nt his contribution we demonstrate that similar CO homologation reactivity may be achieved through exposure of the bdiketiminato magnesium hydride (IV) [5] to one atmosphere of CO and that this and other alkaline earth species enable the highly selective catalytic reduction of the carbon monoxide molecule under similarly mild reaction conditions.…”

“…No further species could be discriminated during continued monitoring of the low-temperature conversion of IV to 1-13 C. Although alternative pathways may be envisaged, including the dimerization of two carbene-like formyl units after reaction of 2 with af urther equivalent of CO,t here is no compelling justification to suggest that the route to compound 1 contrasts with that formerly deduced for the formation of compounds such as II and III. [3] We propose, therefore,t he reaction pathway shown in Scheme 1i nw hich the initial carbonylation product, compound 2,i sr apidly consumed through intramolecular hydride transfer to form adinuclear oxomethylene species 3.Species 3 is prone to C-C coupling through its reaction with af urther molecule of CO while the stereochemistry of the cis-enediolate,c ompound 1, will ensue through a1 ,2-hydrogen shift within species 4,t he selectivity of which is dictated by the anti-periplanar orientation of the C À Hb onds to the carbene lone pair across the OCH 2 CO unit.…”

Reactions of Monomeric [1,2,4-(Me3C)3C5H2]2CeH and CO with or without H2: An Experimental and Computational Study

“…12a The dimeric ytterbium hydride, [tris(3-Me 3 C-5-Me-pyrazolyl)borate] 2 Yb 2 (μ-H 2 ) 2 gives the cis-enediolate on reaction with CO, [Pz' 3 BH)Yb] 2 (μ-OCH=CHO). 12b Recently, the tetrameric yttrium and lutetium dihydrides, [(Me 3 Si)(Me) 4 C 5 ] 4 M 4 (μ-H) 8 (thf), were found to yield [(Me 3 Si)(Me) 4 C 5 ] 4 M 4 (μ-O) on reaction with CO and ethylene; in the case of M = Y, oxomethylene complexes were isolated and characterized. 12c The monomeric metallocenes of thorium, (C 5 Me 5 ) 2 Th(H)(OR), where R = CH(CMe 3 ) 2 or 2,6-(Me 3 C) 2 C 6 H 4 , reacts reversibly with CO at low temperature to give a formyl, (C 5 Me 5 ) 2 Th(COH)(OR), which is spectroscopically detected but not isolated, that reacts with additional CO to give the isolable cis-enediolate, [(C 5 Me 5 ) 2 Th(OR)] 2 (μ-OCH=CHO).…”

The Synthesis of Organometallic YlidesInteraction of Methylenetriphenylphosphorane with Bis(η5-cyclopentadienyl)-zirconium and -hafnium Dichlorides and the Molecular Structure of Bis(η5 -Cyclopentadienyl)chlorozirconylmethylenetriphenylphosphorane

“…For example, bis(^5-cyclopentadienyl)zirconium hydridochloride is a versatile reagent for functionalization of alkenes, dienes, and alkynes [1]. Other complexes of zirconium serve as model compounds for the reduction of carbon monoxide [2], and titanium organometallic complexes play an important role in the Ziegler-Natta polymerization of alkenes [3].…”