Different Coordination Modes of the Ph₂PC_sp³PPh₂ Pincer Ligand in Rhodium Complexes as a Consequence of C_sp³–H Metal Interaction

Starting from commercially available 4,4′-di-<i>tert</i>-butyldiphenylmethane the pincer ligand bis­(4-<i>tert</i>-butyl-2-(diphenylphosphino)­phenyl)­methane (<b>PCP</b>) was prepared in two steps in moderate yield. Treatment of a solution of RhCl₃·3H₂O in a mixture of isopropyl alcohol and toluene with equimolar amounts of <b>PCP</b> gave the dimeric rhodium complex <b>1</b>. In an electrophilic metalation a facially coordinated pincer complex is formed. When <b>PCP</b> is treated with [CODRhCl]₂ in a solution of pyridine, the square-pyramidal complex <b>2</b> is generated where the bis-phosphine <b>PCP</b> acts as bidentate ligand that coordinates in a cis fashion. SnCl₂ inserts into the Rh–Cl bond of <b>2</b>, which results in an oxidative addition of one of the methylene C–H bonds to form the Rh­(III) complex <b>3</b>, where the <b>PCP</b> ligand coordinates in a meridional way. A 2 equiv portion of <b>PCP</b> reacts with 1 equiv of [CODRhCl]₂ in the presence of the electron-donating ligands HPhPC₆H₄NMe₂, PPh₂Py, and PPh₃, respectively, as well as with stanna- and germa-<i>closo</i>-dodecaborate to give the octahedral Rh­(III) complexes <b>4</b>–<b>8</b>. Attempts to remove the HCl with KO^tBu from complexes <b>4</b>–<b>6</b> produces the planar Rh­(I) compounds <b>9</b> and <b>10</b>. No carbene formation has been observed

Intermolecular ¹¹⁹Sn,³¹P Through-Space Spin–Spin Coupling in a Solid Bivalent Tin Phosphido Complex

A bivalent tin complex [Sn­(NP)₂] (NP = [(2-Me₂NC₆H₄)­P­(C₆H₅)]⁻) was prepared and characterized by X-ray diffraction and solution and solid-state nuclear magnetic resonance (NMR) spectroscopy. In agreement with the X-ray structures of two polymorphs of the molecule, ³¹P and ¹¹⁹Sn CP/MAS NMR spectra revealed one crystallographic phosphorus and tin site with through-bond ¹<i>J</i>(^117/119Sn,³¹P) and through-space ^TS<i>J</i>(^117/119Sn,³¹P) spin–spin couplings. Density functional theory (DFT) calculations of the NMR parameters confirm the experimental data. The observation of through-space ^TS<i>J</i>(^117/119Sn,³¹P) couplings was unexpected, as the distances of the phosphorus atoms of one molecule and the tin atom of the neighboring molecule (>4.6 Å) are outside the sum of the van der Waals radii of the atoms P and Sn (4.32 Å). The intermolecular Sn···P separations are clearly too large for bonding interactions, as supported by a natural bond orbital (NBO) analysis