Unique Orbital Symmetry-Driven Cisoid Tilting of the Axial Ligands in Dialkylruthenium(IV) Porphyrins

Abstract

DFT calculations aimed at investigating the diamagnetism of dialkyl/diaryl ruthenium-(IV) porphyrins revealed a unique cisoid tilting of the axial alkyl/aryl groups, which maximizes σ-bonding interactions between the metal and the alkyl/aryl ligands via two specific orbital interactions. Only one such stabilizing orbital interaction is possible for upright and transoid orientations of the axial alkyl/aryl groups.

Electronic structure of cis-Mo(P)(NO)2, where P is a porphyrin: An organometallic perspective of metalloporphyrin–NO complexes

“…1) in which the alkyl groups on opposite sides of the porphyrin dramatically tilt over to one side, relative to the porphyrin normal [1]. Gratifyingly, X-ray crystallographic evidence for just such a structure was available for an Os(IV)-bis(trimethylsilylmethyl) porphyrin, although the experimental researchers attributed the remarkable geometry to steric effects [2].…”

Understanding the unexpected linearity of the - Mn(NO) unit in a phthalocyanine complex: some thoughts on dinitrosylheme intermediates in biology

“…1. Recently, we have found that a similar cisoid tilting of the axial alkyl/aryl groups also occurs for diamagnetic M(P)(R) 2 (M = Ru, Os; R = alkyl, aryl) derivatives [20]. The reason for the cisoid tilting appears to lie in the unique importance of specific metal(d)-alkyl/aryl/ NO bonding interactions in these systems, as shown in Fig.…”

“…Is this work relevant to biology, namely to heme protein function, in any manner? We believe that there may indeed be a common thread -a commonality of metal-ligand orbital interactions -running through much of our recent theoretical studies of metalloporphyrin-nitrosyl [24,18] and organometallic [20] complexes on the one hand and heme protein function on the other. Fig.…”

“…Such an electronic-structural scenario (i.e., nonoccupancy of the d z2 orbital) may be operative in certain trigonal bipyramidal NO complexes [36] which also exhibit nearly linear MNO units and short M-N(NO) distances. Finally, it is gratifying that although we undertook this study as well as our recent studies on dinitrosyl [18] and organometallic [20] complexes with the rather purist goal of simply obtaining a better understanding of their electronic and geometric structures, our findings after all may prove to be biologically relevant. …”

Synthesis, Characterization, and Infrared Reflectance Spectroelectrochemistry of Organoruthenium Nitrosyl Porphyrins

“…38 Such tilting in the latter class of diamagnetic d 4 compounds has been attributed, on the basis of the results of DFT calculations, to the strong trans influence of the alkyl ligands that destabilize a linear axial structure. 39,40 The Ru−N(O) bond length in (T(p-OMe)PP)Ru(NO)Et is 1.825(5) Å (cf. 1.827(5) Å for the minor component), and is longer than that for the related (OEP)Ru(NO)(C 6 H 4 F-p) at 1.807(3) Å which was described as being very long for a (por)Ru−NO bond.…”