The boranes b and c reacted with 2 in a manner similar to a, producing only the desired side-on phosphinoboryl complexes (2b, 2c) and free PCy3. The isolation yields of complexes 2b and 2c were 60% and 74%, respectively. NMR spectroscopic data and XRD analyses of 2b and 2c fully supported the formation of side-on phosphinoboryl complexes (see ESI for details, Figures and). In contrast to experiments with compounds a-c, phosphinoborane d, with less bulky and electron-withdrawing phenyl substituents on the phosphorus atom, reacted with 2 in toluene through the oxidative addition of the B-P bond instead of the B-Br bond to the metal fragment (Scheme 1). Evaporation of the solvent and crystallization from petroleum ether at -20 °C yielded 2d as red crystals along with byproducts such as PCy3 and the hydrido complex [Br(H)Pt(PCy3)2] in a molar ratio of 2:4:1. The complex 2d exhibited solubility in hydrocarbons similar to that of the byproducts, which prevented its purification via crystallization. X-ray analysis revealed that 2d contained two Pt(II) centers connected by two bridging PPh2 phosphido ligands (Fig. ). Additionally, two Cy2NBBr boryl ligands were coordinated to the first platinum atom, while one PCy3 ligand completed the coordination sphere of the second platinum atom. The XRD results aligned with the 31 P{ 1 H} NMR data for 2d, which displayed two coupled doublets ( 2 JPP = 80 Hz): a highly deshielded resonance at 235.3 ppm with two sets of platinum satellites ( 1 JPt1P = 979 Hz, 1 JPt2P = 2780 Hz) attributed to the bridging phosphido ligands, and a second resonance at 61.4 ppm for the PCy3 ligand coupled only to one platinum center ( 1 JPt2P = 2780 Hz). Unlike 1a and 2a-2c, 2d did not show any resonance in the B NMR spectra despite the presence of two boryl ligands. The electron-withdrawing phenyl substituents on the phosphorus atom in the parent phosphinoborane facilitated the heterolytic cleavage of the B-P bond after the nucleophilic substitution of the electron-rich Pt(0) center onto the electrophilic boron atom and additionally stabilized the negative charge of the departing phosphido ligand. To our knowledge, compound 2d is the first example of a transition metal complex containing both phosphido and boryl ligands. All title phosphinoboryl complexes exhibited very similar structural features; therefore, they will be discussed in detail using the representative compound 2a as an example (Fig. ). The phosphinoboryl ligand coordinated to the Pt(II) center in a side-on manner via B1 and P1 atoms, forming a Pt1-B1-P1 triangle. Additionally, the phosphine and bromido ligands coordinated to the metal and were respectively positioned trans to the P1 and B1 atoms of the phosphinoboryl group. The geometry around the Pt1 atom was a distorted square planar, with the P2 and Br1 atoms deflected from the Pt1-B1-P1 plane in opposite directions by 0.411 and 0.321 Å, respectively. | 3