Phosphine-substituted sterically encumbered pyrrolyl ligands – synthesis and reactivity studies

Abstract

The sterically encumbered pyrrolyl KPyr(tBu2) (1-K, Pyr(tBu2) = 2,5-(Me3C)2C4H2N) reacts with PCl3, (iPr)2PCl and Ph2PCl exclusively at the C3-position to yield a series of phosphine-substituted pyrroles HPyr(tBu2R) (R = PCl2 (2-H), (iPr)2P (4-H) and Ph2P (5-H)). Pyrrole 2-H can further be functionalized with MeLi (3 equiv.) to yield LiPyr(tBu2PMe2) (3-Li). The coordination chemistry of these phosphine-substituted pyrroles was explored and the resulting complexes were characterized by various spectroscopic techniques and in some cases using single crystal X-ray diffraction. The neutral pyrroles 4-H and 5-H react cleanly with [Mo(CO)6] to form the κP-coordinate complexes 4-H-Mo(CO)5 and 5-H-Mo(CO)5, respectively. IR spectroscopy of these complexes shows that C3-substitution barely changes the π-acceptor properties of the phosphine moiety. The η(5)-coordination was achieved when pyrrolides 4-K and 5-K were reacted with [Mn(CO)5Br] to give 4-Mn(CO)3 and 5-Mn(CO)3, respectively. The energy of the HOMOs in these three legged-piano stool complexes decreases on PPh2-substitution (5-Mn(CO)3) stabilizing the Mn-CO bonds, whereas the inverse effect is noticed for P(iPr)2-substitution (4-Mn(CO)3).

Synthesis and Electronic Ground-State Properties of Pyrrolyl-Based Iron Pincer Complexes: Revisited

“…Several factors have contributed to this development, including readily modifiable steric and electronic properties of the pincer architecture and the high thermal stability of the resulting metal compounds. These advantageous properties have led to many applications in small-molecule activation and catalysis. − Within this group, pincer complexes of 3d transition metals are particularly appealing and various catalysts have been developed for hydrofunctionalization, − cross-coupling, , C–H bonding, CO 2 , or N 2 activation and functionalization, − and dehydrogenation reactions. , These advances stimulated our interest in this area, and we extended our previous work on sterically encumbered pyrrolyl ligands − to pyrrolyl-based PNP pincer systems ( I ; Chart ). In 2012, the phenyl-substituted pyrrolyl-based PNP ligand was introduced independently by the groups of Tonzetich, Gade, and Mani and applied for the synthesis of nickel and palladium compounds.…”

Teaching Ferrocenium How to Relax: A Systematic Study on Spin–Lattice Relaxation Processes in tert‐Butyl‐Substituted Ferrocenium Derivatives

“…Our group has been interested in organometallic transition‐metal compounds for some time, and we usually employ sterically very demanding cyclopentadienyl, pyrrolyl,[9h], or pentadienyl ligands to stabilize metal centers. In the course of these investigations, we have also prepared iron half‐sandwich compounds,[15b], [15c], [15f], [15g], [15n], diazaferrocenes.…”

Coordination chemistry of sterically encumbered pyrrolyl ligands to chromium(ii): mono(pyrrolyl)chromium and diazachromocene formation

“…6,7,19,20 Recently, we have initiated a research program on sterically encumbered pyrrolyl systems with an emphasis on comparing them with their cyclopentadienyl analogues, with respect to their ability to stabilize halfsandwich complexes. [21][22][23] Herein, we report our observations on the coordination chemistry of bulky pyrrolyls (Chart 1) with Cr(II) and briefly discuss the reactivity of pyrrolyl chromium(II) half-sandwich complexes in the polymerization/oligomerization of ethylene.…”