Reactivity Profile of a Peri-Substitution-Stabilized Phosphanylidene-Phosphorane: Synthetic, Structural, and Computational Studies

The reactions of peri-substitution-stabilized phosphanylidene-phosphorane 1 with [AuCl­(tht)] or [PtCl2(cod)] afford binuclear complexes
[((1)­(AuCl)2)2] 2 and
[((1)­(PtCl2))2] 3,
in which four electrons of the ligand are used in bonding to two metal
atoms in the bridging arrangement. Reactions of 1 with
[Mo­(CO)4(nbd)] or (RhCl2Cp*)2 afford
mononuclear complexes [(1)2Mo­(CO)4] 4 and [(1)­RhCl2Cp*] 5, in which two electrons of the ligand are used to form terminal
complexes. Formation of these complexes disrupts the negative hyperconjugation
at the P–P bond to various extents, which is mirrored by variations
in their P–P bond distances (2.179(4)–2.246(4) Å).
The P–P bond is ruptured upon formation of Pd diphosphene complex 6, which is likely to proceed through a phosphinidene intermediate.
In air, 1 is fully oxidized to phosphonic acid 7. Reactions of 1 with chalcogens under mild
conditions generally afford mixtures of products, from which the trithionated 8, dithionated 9, diselenated 10, and monotellurated 11 species were isolated. The bonding
in the chalcogeno derivatives is discussed using DFT (B3LYP) and natural
bond orbital analysis, which indicate a contribution from dative bonding
in 8–10. The buttressing effect of
the peri backbone is shown to be an essential factor
in the formation of the single push–double-pull bis­(borane) 13. This is demonstrated experimentally through a synthesis
parallel to that used to make 13, but lacking the backbone,
which leads to different products. The P–P bond distances in
the reported products, as well as additional species, are correlated
with Wiberg bond indices, showing very good agreement for a variety
of bonding modes, including the negative hyperconjugation.