Synthesis of tetrakis[(tri‐tert‐butylphosphane)gold(I)]phosphonium salts and crystal structure of the tetraphenylboroxinate salt {[(tBu)₃PAu]₄P}⁺ [O(PhBO)₂BPh₂]^—

The reaction of (Me₂Si)₃P with {[(tBu)₃PAu]₃O}⁺ BF₄^– in tetrahydrofuran at —78C affords the compound {[(tBu)₃‐PAu]₄P}⁺ BF₄^— (1a) in high yield. This product is converted into the tetraphenylborate salt (1b) by treatment with Na[BPh₄]. The two compounds have been identified on the basis of their analytical and spectroscopic data, but could not be crystallized. In attempts to prepare single crystals of 1b, a crystalline salt {[(tBu)₃PAu]₄P}⁺ [O(PhBO)₂BPh₂]^— (1c) has been obtained in very small quantities, probably by partial anion hydrolysis. A single crystal X‐ray diffraction study of 1c CH₂Cl₂ shows the compound to be built up of cations with a strongly distorted tetrahedral (PAu)₄P skeleton and anions with a planar six‐membered boroxine ring. Two of the phenyl groups are attached to two trigonal‐planar boron atoms and the other two phenyl groups to the third (tetrahedral) boron atom of the heterocycle. The origin of the peculiar cation structure is discussed in the light of findings with related ammonium‐ and arsonium‐centered gold clusters.