Impact of\nHalide (Cl vs I) Identity on the Preferred\nPositioning of Substituents between Al and M (M = Co, Rh, Ir) in PAlP\nPincer Complexes

Protolysis of AlMe<sub>3</sub> or AlEt<sub>3</sub> with\n2-diisopropylphosphinopyrrole\n(<b>1</b>) resulted in alane/bis(phosphine) pincer ligands containing\ntwo flanking phosphines and a central Al–Me (<b>2-Me</b>), Al–Et (<b>2-Et</b>) unit. Reactions of <b>2-Me</b> with [(COD)MI]<sub>2</sub> (COD = 1,5-cyclooctadiene; M = Rh or\nIr) in the presence of pyridine produced pincer complexes (<b>3–Rh–I</b> and <b>3–Ir–I</b>) with M supported by the PAlP\ntridentate ligand, and pyridine, methyl, and iodide as monodentate\nligands for Al or M. The analogous reaction of <b>2-Et</b> with\n[(COD)MI]<sub>2</sub> and pyridine resulted in the formation of the\nanalogous compounds <b>4–Rh–I</b> and <b>4–Ir–I</b> with hydride in place of methyl. DFT calculations were used to analyze\nthe thermodynamic preferences for the positioning of pyridine, methyl\nor hydride, and the halide (chloride or iodide) on M vs Al. Cobalt\nwas included with Rh and Ir among M for the purposes of DFT calculations.\nTheoretical studies suggested that different isomers are preferred\nfor the iodide complexes (M–I and Al–Py) than for the\nchloride ones (M–py and Al–Cl, previously reported for\nRh and Ir). X-ray structural study of <b>3–Rh–I</b> and analysis of the <sup>1</sup>H NMR data of the Rh and Ir compounds\nin benzene corroborated these predictions.