Preparation and Structure of Hexakis[(trialkylphosphane)aurio(I)]methanium(2+) Salts [(LAu)₆C]²⁺(X^‐)₂ with LEt₃P, iPr₃P and XBF₄^‐, B₃O₃F₄^‐

Hexaaurated carbon complexes of the type [(R₃PAu)₆C](BF₄)₂, REt (2a), iPr (2b) have been prepared by the reaction of the appropriate (phosphane)gold(I) chlorides R₃PAuCl (1a and 1b) with tetrakis(dimethoxyboryl)methane, ¹³C–enriched at the central carbon atom, in the presence of excess of CsF in HMPT at room temperature. The products 2a and 2b are characterized by standard spectroscopic methods including direct detection of the interstitial C atoms by ¹³C–NMR spectroscopy. The crystal structure of the compound [(iPr₃PAu)₆C](B₃O₃F₄)₂ · 3 CH₂Cl₂ (3), obtained from partial (anion) hydrolysis has been determined. It contains dications with a central carbon atom surrounded by six (phosphane)gold(I) units. The edges of the CAu₆ octahedron represent short Au–Au contacts (aprox. 3.0 Å), which strongly contribute to the formation and stability of these hypercoordinated species. Attempts to prepare a corresponding hexaauriomethanium dication starting from tBu₃PAuCl (1c) failed owing to the bulkiness of the (tri‐tert‐butylphosphane)gold(I) unit. The X–ray structure analysis for 1c verifies an extremely crowded environment of the gold atom with small Au—P—C angles of only 107° leading to efficient shielding of the metal atom by methyl groups.