S1 Electronic Supporting Information Magnesium Hydridotriphenylborate [Mg(thf) 6 ][HBPh 3 ] 2 : A Versatile Hydroboration Catalyst Debabrata Mukhejee, a Satoru Shirase, b Thomas P. Spaniol, a Kazushi Mashima, b and Jun Okuda a, * a Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52056 Aachen, Germany. b Graduate School of Engineering Science, Osaka University, Toyonoka, Osaka 560-8531, Japan. Table of Contents General remarks...................................................................................................S1 Synthetic procedures and spectroscopic data for 1, 9, and 10.............................S1 Catalysis...............................................................................................................S8 Crystal structure analysis.....................................................................................S20 References............................................................................................................S21 General remarks. All manipulations were performed under argon atmosphere using standard Schlenk or glove box techniques. Prior to use, glassware was dried overnight at 130 °C and solvents were dried, distilled and degassed using standard methods. NMR measurements were performed on a Bruker DRX 400 at ambient temperature unless otherwise mentioned. The chemical shifts (δ ppm) in the 1 H and 13 C{ 1 H} NMR spectra were referenced to the residual proton signals of the deuterated solvents and reported relative to tetramethylsilane. S1 Abbreviations for NMR spectra: s (singlet), d (doublet), t (triplet), q (quartet), sep (septet), br. (broad). IR spectra were measured on KBr pellets using an AVATAR 360 FT-IR spectrometer. Abbreviations for IR spectra: w (weak), m (medium), s (strong), br. (broad). BPh 3 (95%) was purchased from abcr and recrystallized from Et 2 O solution at 35 °C. [Mg{N(SiHMe 2 ) 2 } 2 ] was synthesized following literature procedure. S2 All the substrates and HBpin were purchased from the suppliers like Sigma-Aldrich, Alfa Aesar, and abcr. CO 2 (purity level 5.0, equals to 99.990% purity) was purchased from Westfalen, Germany and passed through a column of P 4 O 10 with moisture indicator while using in the Schlenk line. Elemental analyses were performed on an elementar vario EL machine. X-ray diffraction data were collected on a Bruker APEX II diffractometer. Single crystal diffraction data of 9 is reported in crystallographic information file (cif) accompanying this document. [Mg(thf) 6 ][HBPh 3 ] 2 (1). [Mg{N(SiHMe 2 ) 2 } 2 ] (0.100 g, 0.346 mmol) and BPh 3 (0.168 g, 0.694 mmol) were dissolved together in 5 mL of THF. The solution mixture was stirred at room temperature for 12 h, Electronic Supplementary Material (ESI) for ChemComm. This journal is © The Royal Society of Chemistry 2016