The reaction of closo-[B 10 H 10 ] 2− with [PtCl 2 (PPh 3 ) 2 ] in MeOH at reflux affords the B-methoxy substituted 11-vertex nido-platinaborane compound [(PPh 3 ) 2 PtB 10 H 10 -8-H 0.5 (OCH 3 ) 0.5 -10-(OCH 3 )] (1) and the known species [(PPh 3 ) 2 PtB 10 H 11 -8-(OCH 3 )] (2) and 1,6-(PPh 3 ) 2 B 10 H 8 (3). The same reaction under solvothermal condition gives the partially degraded diplatinaborane [(PPh 3 ) 2 (μ-PPh 2 )Pt 2 B 9 H 7 -3,9,11-(OMe) 3 ] (4) with a novel nido-Pt 2 B 9 H 10 skeleton. The new metallaborane compounds have been characterized by spectroscopic methods and single-crystal X-ray analyses. In particular, computational/theoretical chemistry supports the ultimate structural confirmation of 4. The structures of these metallaboranes exhibit interesting intra- and/or intermolecular C–H⋯O hydrogen bonding interactions.