INSERTION REACTIONS OF METAL-CARBONYL ANIONS WITH METHYL FORMATE IN THE GAS-PHASE AS REVEALED BY C-13-LABELING AND D-LABELING

The gas-phase reactions of coordinatively unsaturated metal carbonyl a nions (M(CO)n-, M = Cr, Mn, Fe, Co, n = 0-3 and Co(CO)nNO-, n = 0-2) w ith unlabeled and D- and C-13-labeled methyl formate have been studied with Fourier transform ion cyclotron resonance mass spectrometry. The reactions proceed in most instances by loss of one or more CO molecul es from the collision complex. In the reactions of the dicarbonyl and tricarbonyl anions with (HCOOCH3)-C-13, part of the eliminated carbon monoxide molecules contain the label revealing the occurrence of initi al insertion of the metal center into the bonds adjacent to the carbon yl function of the substrate with formation of five- or six-coordinate intermediates, respectively. In addition, the Mn(CO)3-, Fe(CO)2-, and Co(CO)2- ions react by the loss of methanol and a [C,H-2,O] neutral s pecies. The D- and C-13-labeling show that methanol is expelled in a r eductive elimination from a five- or six-coordinate species, whereas t he [C,H-2,O] loss is a more complex process possibly involving the com peting losses of formaldehyde and CO + H-2. In the reaction of Fe(CO)3 - with (HCOCCH3)-C-13, a facile consecutive exchange of all three CO l igands of the reactant ion for (CO)-C-13 is observed. This novel react ion appears to involve initial insertion into the (HCO)-C-13-OCH3-bond followed by facile hydrogen shifts from the formyl ligand to a CO lig and prior to the loss of unlabeled methyl formate.