Transition Metal Complexes of PNP and PNN Ligands: Synthesis and Catalytic Applications in Hydrophosphination of Terminal Alkynes

ABSTRACT In this study, we report the synthesis and structural characterization of a series of transition metal complexes derived from two pincer‐type ligands: (o ‐PPh 2) C 6 H 4 C (O) NH (C 9 H 6 N) (1) and (o ‐Ph 2 PC 6 H 4 C (O) N (H) C 6 H 4 PPh 2 ‐ o) (2). Treatment of Ligand 1 with Rh (acac) (CO) 2 afforded rhodium pincer complex Rh (CO) (o ‐PPh 2) C 6 H 4 C (O) N (C 9 H 6 N) κ 3 ‐ P, N, N (3). Ligand 1, upon reaction with Ru (H) (CO) (Cl) (PPh 3) 3 in THF, yielded the ruthenium complex Ru (PPh 3) (CO) (Cl) (o ‐PPh 2) C 6 H 4 C (O) N (C 9 H 6 N) κ 3 ‐ P, N, N (4), while its reaction with Ru (Cl) 2 (PPh 3) 3 in methanol afforded a Ru III complex, Ru (CH 3 OH) (Cl) 2 (o ‐PPh 2) C 6 H 4 C (O) N (C 9 H 6 N) κ 3 ‐P, N, N (5). Ligand 2, when reacted with CuI in a 1: 1 M ratio in a CH 2 Cl 2 /CH 3 CN (1: 1 v/v) mixture, yielded the dimeric complex CuI (o ‐PPh 2) C 6 H 4 C (O) N (H) CH 2 C 6 H 4 (o ‐PPh 2) 2 (6). Increasing the CuI to ligand ratio to 2: 1 yielded the tetrameric complex Cu 4 (μ 2 ‐I) 2 (μ 3 ‐I) 2 (o ‐PPh 2) C 6 H 4 C (O) NCH 2 C 6 H 4 (o ‐PPh 2) 2 ‐ P, P (7). The reaction of Ligand 2 with two equivalents of AuCl (SMe 2) produced a binuclear gold complex, AuCl (o ‐PPh 2) C 6 H 4 C (O) N (H) CH 2 C 6 H 4 { (o ‐PPh 2) AuCl (8). Furthermore, Ligand 2 underwent complexation with Rh (acac) (CO) 2 and Mn 2 (CO) 10 to afford PNP‐type pincer complexes RhCO (o ‐PPh 2) C 6 H 4 C (O) NCH 2 C 6 H 4 (o ‐PPh 2) κ 3 ‐ P, N, P (9) and Mn (CO) 3 (o ‐PPh 2) C 6 H 4 C (O) NCH 2 C 6 H 4 (o ‐PPh 2) κ 3 ‐ P, N, P (10) respectively. Notably, the rhodium PNN pincer Complex 3 was successfully employed as a catalyst in the additive‐free hydrophosphination of phenylacetylenes, providing a more straightforward and operationally simple methodology for this transformation.