Flexible interactions of the rare-earth elements Y, La, and Lu with phosphorus in metallacyclohexane rings

A geometrically flexible bifunctional (bis)aminophosphine ligand was synthesized in a three-component, one-pot Kabachnik-Fields reaction using tert butylphosphine, paraformaldehyde, and 3,5-dimethyl aniline. The product, bis((3,5-dimethylphenyl)aminomethyl) tert butylphosphine (ArBiAMP t Bu), containing two secondary amines and a tertiary phosphine, was isolated in good yields. Deprotonation of both N-H groups with (trimethylsilyl)methylpotassium (K-CH2SiMe3), followed by salt metathesis with LaI3, YI3, and LuI3 generated the corresponding MI(ArBiAMP t Bu)(thf)3 complexes (M = Y (1), La (2), and Lu (3)) in good yields. A sterically encumbered indene, 1,3-diisopropyl-4,7-dimethyl-1H-indene, iPrMeInd, was deprotonated in situ and installed via salt-metathesis to generate the organometallic series of η5-indenide complexes, M(ArBiAMP t Bu)(η5-iPrMeInd)(thf) (M = Y (4), La (5), and Lu (6)). 1H, 31P, 13C, and 89Y NMR experiments, IR spectroscopy, and single crystal X-ray diffraction (SC-XRD), were used to characterize these complexes. The Y-P coupling constant was found to be variable depending on the modifiable coordination environment of the metal center, indicating potential as both a spectroscopic handle as well as providing insight into the influence of additional ligands on the metal center.

31P Chemical Shifts in Ru(II) Phosphine Complexes. A Computational Study of the Influence of the Coordination Sphere

The NMR chemical shift has been the most versatile marker of chemical structures, by reflecting global and local electronic structures, and is very sensitive to any change within the chemical species. In this work, Ru(II) complexes with the same five ligands and a variable sixth ligand L (none, H₂O, H₂S, CH₃SH, H₂, N₂, N₂O, NO⁺, C═CHPh, and CO) are studied by using as the NMR reporter the phosphorus P_A of a coordinated bidentate P_A-N ligand (P_A-N = o-diphenylphosphino-N,N'-dimethylaniline). The chemical shift of P_A in RuCl₂(P_A-N)(PR₃)(L) (R = phenyl, p-tolyl, or p-FC₆H₄) was shown to increase as the Ru-P_A bond distance decreases, an observation that was not rationalized. This work, using density functional theory (DFT) calculations, reproduces reasonably well the observed ³¹P chemical shifts for these complexes and the correlation between the shifts and the Ru-P_A bond distance as L varies. An interpretation of this correlation is proposed by using a natural chemical shift (NCS) analysis based on the natural bonding orbital (NBO) method. This analysis of the principal components of the chemical shift tensors shows how the σ-donating properties of L have a particularly high influence on the phosphine chemical shifts.

Experimental characterization of the hydride 1H shielding tensors for HIrX2(PR3)2 and HRhCl2(PR3)2: extremely shielded hydride protons with unusually large magnetic shielding anisotropies

The hydride proton magnetic shielding tensors for a series of iridium(III) and rhodium(III) complexes are determined. Although it has long been known that hydridic protons for transition-metal hydrides are often extremely shielded, this is the first experimental determination of the shielding tensors for such complexes. Isolating the (1)H NMR signal for a hydride proton requires careful experimental strategies because the spectra are generally dominated by ligand (1)H signals. We show that this can be accomplished for complexes containing as many as 66 ligand protons by substituting the latter with deuterium and by using hyperbolic secant pulses to selectively irradiate the hydride proton signal. We also demonstrate that the quality of the results is improved by performing experiments at the highest practical magnetic field (21.14 T for the work presented here). The hydride protons for iridium hydride complexes HIrX2(PR3)2 (X = Cl, Br, or I; R = isopropyl, cyclohexyl) are highly shielded with isotropic chemical shifts of approximately -50 ppm and are also highly anisotropic, with spans (=δ11 - δ33) ranging from 85.1 to 110.7 ppm. The hydridic protons for related rhodium complexes HRhCl2(PR3)2 also have unusual magnetic shielding properties with chemical shifts and spans of approximately -32 and 85 ppm, respectively. Relativistic density functional theory computations were performed to determine the orientation of the principal components of the hydride proton shielding tensors and to provide insights into the origin of these highly anisotropic shielding tensors. The results of our computations agree well with experiment, and our conclusions concerning the importance of relativistic effects support those recently reported by Kaupp and co-workers.

Solid state NMR studies and chemical shift calculations of a gold(I) complex with a diphosphacyclobutadiene cobaltate sandwich anion

The (31)P and (13)C solid state nuclear magnetic resonance spectra of a neutral gold(I) complex with bis(diphosphacyclobutadiene) cobaltate anions, [Au{Co(P2C2tPent2)2}2(PMe3)2], are reported. Complete (31)P resonance assignments have been derived from saturation transfer, radio-frequency driven recoupling (RFDR) and RTOBSY experiments and confirmed further by ab-initio calculations of magnetic shielding tensors by density functional theory, with consideration of relativistic effects. Coordination of the diphosphacyclobutadiene ring with gold(I) results in a high-frequency shift of the (31)P signal of the directly coordinated P atom, whereas a low-frequency shift is observed for the P atom at the opposite end of that ring. Based on these results, a previous assignment made for the complex salts [Au(PMe3)4][Au{Co(P2C2Ad2)2}2] and [K(18-crown-6)(thf)2][Au{Co(P2C2Ad2)2}2] (Ad=adamantyl) must be corrected.

Solid-state phosphorus-31 NMR spectroscopy of a multiple-spin system: an investigation of a rhodium-triphosphine complex

Phosphorus-31 NMR spectra of solid [tris(dimethylphenylphosphine)](2,5-norbornadiene) rhodium(I) hexafluorophosphate have been acquired at several applied magnetic field strengths. The phosphorus nuclei of the three phosphine ligands are spin-spin coupled to each other and to 103Rh, resulting in complex NMR spectra; however, the three phosphorus chemical shift (CS) tensors were determined through the analysis of NMR spectra of slow magic angle spinning and stationary samples. Spectra of spinning samples in rotational resonance and two-dimensional 31P NMR spectra were particularly useful for determining the magnitudes of the indirect spin-spin couplings, and to probe their signs. Despite being in similar environments, the three phosphorus nuclei of the phosphine ligands have distinct CS tensors. In particular, the spans of these tensors, delta11-delta33, range from 80 to 176 ppm. The phosphorus CS tensors have been assigned to specific sites determined by X-ray crystallography, based on a combination of the experimental results and the results of quantum chemical calculations of the phosphorus shielding and 2J(31P,31P) values. The effect of coordination of dimethylphenylphosphine with rhodium has been investigated by comparing calculated phosphorus CS tensors for the uncoordinated ligand with those obtained for the ligands in the complex.

Diligating Tripodal Amido-Phosphine Ligands: the Effect of a Proximal Antipodal Early Transition Metal on Phosphine Donor Ability in a Building Block for Heterometallic Complexes

The ligand precursors P(CH2NH-3,5-(CF3)2C6H3)3 (1a), P(CH2NHPh)3 (1b), and P(CH2NH-3,5-Me2C6H3)3 (1c), react with the reagents Ti(NMe2)4 and tBuN=Ta(NEt2)3 to generate metal complexes of the type P(CH2NAr(R))3TiNMe2 (2a-c) and P(CH2NAr(R))3Ta=NtBu (3a-c) (where Ar(R) = 3,5-(CF3)2C6H3, Ph, and 3,5-Me2C6H3). Due to ring strain, the phosphine lone pair cannot chelate and is available to bind a second metal, and this feature can be utilized to synthesize heterometallic polynuclear complexes. The 31P chemical shifts observed upon complexation of the early transition metals to the amido donors are large and in the opposite direction expected for the increased C-P-C bond angles in these complexes; these unusual shifts are due to P-Ti and P-Ta distances that are significantly shorter than the sum of van der Waals radii. The reaction of 2c with Ni(CO)4 produces at first the bimetallic complex (CO)3Ni[P(CH2N-3,5-Me2C6H3)3TiNMe2] (4c), which gradually converts to the trimetallic complex (CO)2Ni[P(CH2N-3,5-Me2C6H3)3TiNMe2]2 (5c). The effect of the complexation of Ti and Ta fragments on the donor ability of the phosphine ligand was determined by the preparation of the bis-phosphine complexes trans-L(2)Rh(CO)Cl, (where L = 1a-c, 2a-c, and 3a-c) prepared by the reaction of the appropriate phosphine with [Rh(CO)2(mu-Cl)]2, and a measurement of the resultant CO stretching frequencies. Surprisingly, the complexes with the larger C-P-C angles are significantly poorer donors. Density functional theory calculations were performed to determine what factors affect the donor ability of the phosphine and if through-space interactions might play an important role in the observed electronic properties.