Coordinatively unsaturated transition metal complexes are one of the most important intermediates in organometallic chemistry because of their reactivity towards a variety of ligands. A vacant coordination site on the metal center can accept a substrate or can cleave a variety of chemical bonds to allow metal-catalyzed reactions. Among the bond cleavage reactions, oxidative addition [1] of non-polar (H À H, C À H) or polar (O À H, N À H) bonds to coordinatively unsaturated complexes is one of the most important elementary reactions. In contrast to the well-studied HÀH bond cleavage employed for homogeneous hydrogenation in industry, [2] the other three reactions are still not ready to be used in bulk processes despite their potential for new industrial uses, such as the dehydrogenation of alkanes and the addition of heteroatoms to C À C multiple bonds. [3] Recently, rhodium and iridium complexes with a meridional and tridentate pincer ligand have gained attention because of their ability to undergo oxidative addition to these CÀC multiple bonds. [3b, 4] From a mechanistic point of view, a T-shaped, 14-electron pincer complex possessing an open coordination site is an assumed intermediate in the reaction of such complexes with X À H bonds (X = C or a heteroatom). Although some pincer-ligated fourth period transition metal complexes possessing a T shape have been synthesized and characterized as stable species, owing to the partial occupation of a d orbital with high-spin character, [5] similar fifth and sixth period transition metal complexes have been elusive because of their high reactivity at the vacant d orbital on the metal center. As the only exception and as a model of such a T-shaped rhodium complex, a methane-coordinated cationic [(PNP)Rh(CH 4 )] + species with a weak C À H s coordination and its dynamic properties were characterized by NMR spectroscopy. [6] Recently, we have reported the synthesis of a boroncontaining PBP pincer ligand and its complexation with iridium metal to show the strong s-donation ability of the PBP ligand. [7] Considering the very strong trans influence of the boryl ligand, a low-coordinated species having a vacant site in the position trans to the boryl ligand may be stabilized. Herein, we report the synthesis, crystal structures, and reactivity of a PBP-rhodium complex stabilized by intermolecular C-H s-coordination, which acts as a fourth ligand.A PBP pincer ligand was introduced to a rhodium center by the reaction of precursor hydroborane 1 with [Rh(cod)Cl] 2 (cod = 1,5-cyclooctadiene) to give the corresponding [(PBP)Rh(H)]Cl complex 2 in 60 % yield (Scheme 1). Experimental and theoretical study of 2 showed that 2 was a boryl complex possessing a very weak B-H interaction, as can be seen in the following data. The rhodium complex 2 showed a characteristic hydride signal at d H À22.09 as a broad doublet of triplets resonance in the 1 H NMR, coupled with 31 P, 103 Rh, and 11 B. On the other hand, decoupling of the 11 B nucleus in the 1 H NMR spectra induced a sharpening of th...