A (carbonmonoxy) heme complex with a weak proximal bond. Molecular stereochemistry of carbonyl(deuteroporphinato)(tetrahydrofuran)iron(II)

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Abstract
The synthesis and structural characterization of a 6-coordinate (carbonmonoxy)(porphyrin)Fe(II), carbonyl(deuteroporphinato)(tetrahydrofuran)Fe(II), is described. The choice of tetrahydrofuran as the 6th ligand represents one of the weakest field and weakest binding ligands possible and leads to stronger than usual bonding of CO to the heme. The Fe.sbd.C(CO) bond distance is 1.706 .ANG., unusually short. The Fe.sbd.O(THF) bond distance in the low-spin complex is 2.127 .ANG.. The Fe.sbd.C.sbd.O and O.sbd.Fe.sbd.C groups are essentially linear with angles of 178.3.degree. and 177.4.degree., respectively. The Fe atom is displaced out of plane 0.10 .ANG. toward the tightly bound CO. The different CO stretching frequencies observed in myoglobin might result from modulating the bonding of the histidine trans to CO. Crystal data are reported.