Unprecedented Coordination of 4,4′,5,5′-Tetramethyl-2,2′-biphosphinine Doubly Bridging over an Open Triosmium Core

Abstract

The crystal structure of the novel cluster [Os3(CO)10(4,4′,5,5′‐tetramethyl‐2,2′‐biphosphinine)] reveals an unprecedented coordination mode of the biphosphinine ligand that occupies a doubly‐bridging position spanning the open osmium triangle. The cluster is photostable, pointing to a localization of the lowest‐energy electronic transition largely on the negatively charged biphosphinine ligand.

Bonding and Redox Properties of [Os3(CO)9(tmbp)(L)] (tmbp=4,4′,5,5′-tetramethyl-2,2′-biphosphinine; L=CO, PPh3) Clusters with an Unprecedented Electron-Deficient Metallic Core and Doubly Bridging Biphosphinine Dianion

“…[26,31] The difference in the character of the lowest-energy electronic transitions explains the previously reported absence of solvatochromism for the corresponding visible absorption band of 1, and the lacking photoreactivity. [13] The same behavior and conclusions essentially apply for 2. Even though the calculated energies for the visible electronic transitions deviate from the experimental values, the trends are correct.…”

“…The single-crystal X-ray studies of clusters 1 [13] and 2 (details in Experimental Section) revealed that the overall structures of these compounds are very close, both involving highly unusual coordination of tmbp ( Figure 1, Table 1, see also Scheme 1).…”

“…The synthesis of the cluster [Os 3 (CO) 10 (tmbp)] 1, was communicated previously. [13] Synthesis of [Os 3 (CO) 9 (tmbp)(PPh 3 )] (2): A solution of [Os 3 (CO) 10 (tmbp)] (1) (87 mg, 0.079 mmol) and excess PPh 3 (62 mg, 0.24 mmol) in THF (60 mL) was stirred for 30 min. No thermal reaction was observed during this time.…”

“…[7] The fairly different electronic properties of tmbp and bpy inspired us to attempt the synthesis of the cluster [Os 3 -(CO) 10 (sP,sP'-tmbp)], so as to perform comparative spectroscopic, photochemical, and electrochemical studies. However, instead of the intended product, a structural isomer was obtained, [13] presenting the first example of a biphosphinine coordinated to three transition metal centers as a doubly bridging ligand (cluster 1 and and its PPh 3 -derivative 2 in Scheme 1). To obtain a good insight into the unusual bonding properties of clusters 1 and 2, a DFT [14] study, using the ADF program, [15] was performed.…”

“…To obtain a good insight into the unusual bonding properties of clusters 1 and 2, a DFT [14] study, using the ADF program, [15] was performed. The computed models were based on the crystal structure of 1, reported in a preceding communication, [13] and that of 2, which is presented in this paper. The redox behavior of the two clusters was also investigated in detail and will be compared with that of [Os 3 (CO) 10 (bpy)] and nonsubstituted [Os 3 (CO) 12 ].…”