Monoanionic Anilidophosphine Ligand in Lanthanide Chemistry: Scope, Reactivity, and Electrochemistry

Abstract

We present the synthesis of a series of new lanthanide(III) complexes supported by a monoanionic bidentate anilidophosphine ligand (N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide, short PN − ). The work comprises the characterization of a variety of heteroleptic complexes containing either one or two PN ligands as well as a study on further functionalization possibilities. The new heteroleptic complexes cover selected examples over the whole lanthanide(III) series including lanthanum, cerium, neodymium, gadolinium, terbium, dysprosium, and lutetium. In case of the two diamagnetic metal cations lanthanum(III) and lutetium(III), we have furthermore studied the influence of the lanthanide ion (early vs. late) on the reactivity of these complexes. Thereby we found that the radius of the lanthanide ion has a major influence on the reactivity. Using sterically demanding, multidentate ligand systems, e.g., cyclopentadienide (Cp − ), we found that the lanthanum complex La(PN) 2 Cl (1-La) reacts well to the corresponding cyclopentadienide complex, while for Lu(PN) 2 Cl (1-Lu) no reaction was observed under any conditions tested. On the contrary, employing monodentate ligands such as mesitolate, thiomesitolate, 2,4,6-trimethylanilide or 2,4,6-trimethylphenylphosphide, results in the clean formation of the desired complexes for both lanthanum and lutetium. All complexes have been studied by various techniques, including multi nuclear NMR spectroscopy and X-ray crystallography. 31 P NMR spectroscopy was furthermore used to evaluate the presence of open coordination sites on the complexes using coordinating and noncoordinating solvents, and as a probe for estimating the Ce−P distance in the corresponding complexes. Additionally, we present cyclic voltammetry (CV) data for Ce(PN) 2 Cl (1-Ce), La(PN) 2 Cl (1-La), Ce(PN)(HMDS) 2 (8-Ce) and La(PN)(HMDS) 2 (8-La) (with HMDS = hexamethyldisilazide, (Me 3 Si) 2 N − ) exploring the potential of the anilidophosphane ligand framework to stabilize a potential Ce(IV) ion.

Unprecedented η3-Coordination and Functionalization of the 2-Phosphaethynthiolate Anion at Lanthanum(III)

“…While the CCAAC=C=P unit is almost linear (C100-C1-P5 173.8(1)°), the angle around the phosphorus atom is strongly bent (C1-P5-S1 111.1(5)°). The La1-S1 distance was found to be 2.950(2) Å and is slightly longer compared to a reported lanthanumsulfur single bond with the same supporting ligand (2.718(1) Å), [15] indicating a reduced negative charge on the sulfur atom and a potential partial conjugation of the CCAAC=C=P unit with the P-S bond. This would be in line with the P5-S1 bond length of 2.081(3) Å, which lies in between the values for a S=P double (≈1.95 Å) [28] and S-P single bond (≈2.12 Å).…”

“…[12] This first example demonstrated the potential difficulties to be encountered in [SCP]coordination chemistry: Due to the unusually high negative charge density on the central carbon atom of the [SCP]anion (natural bond orbital atomic charges correspond to -0.28 for S, -0.74 for C and 0.03 for P), [13] only a mixture of S-and P-bound isomers could be obtained, which decomposed at room temperature within four days. We have recently begun to investigate the chemistry of anilidophosphine-supported lanthanum(III) complexes of the general formula (PN)2LaX with X = Cl (1-Cl) and I (1-I), [15] and have shown them to be versatile precursors for the synthesis of pentacoordinate lanthanum(III) primary phosphido and sulfido complexes (PN)2La(EMes) (E = PH, S). Due to the insertion reactivity of the La-P phosphide bond, the former allowed us to construct phosphaureate and phosphathioureate ligands, which can be used to build unprecedented heterobimetallic systems.…”

Isocyanate Insertion into a La–P Phosphide Bond: A Versatile Route to Phosphaureate-Bridged Heterobimetallic Lanthanide–Coinage-Metal Complexes

“…On consideration of the NMR spectroscopic advantages of diamagnetic lanthanum(III) compounds and the straightforward multigram-scale synthesis of the respective chloride precursor complex, 76 the primary phosphido complex 1 was chosen as the starting point for the evaluation of our targeted synthesis route. The first step of the reaction sequence, namely the insertion of either phenyl isocyanate or phenyl isothiocyanate into the La–P phosphide bond in 1 ( Scheme 3 ), was found to proceed quickly at room temperature.…”

“…A similar one-dimensional polymeric chain structure has been previously reported for the potassium salt KPN . 76 …”

η3‐Coordination and Functionalization of the 2‐Phosphaethynthiolate Anion at Lanthanum(III)**

“…We have recently begun to investigate the chemistry of anilidophosphine‐supported lanthanum(III) complexes of the general formula (PN) 2 LaX with X=Cl ( 1‐Cl ) and I ( 1‐I ), [15] and have shown them to be versatile precursors for the synthesis of pentacoordinate lanthanum(III) primary phosphido and sulfido complexes (PN) 2 La(EMes) (E=PH, S). Due to the insertion reactivity of the La−P phosphide bond, the former allowed us to construct phosphaureate and phosphathioureate ligands, which can be used to build heterobimetallic systems [16] .…”