Phosphinidene Reactivity of a Transient Vanadium PN Complex

Toward
the preparation of a coordination complex of the hetero­diatomic
molecule PN, PN-V­(N­[tBu]­Ar)3 (1, Ar = 3,5-Me2­C6H3), we report the use of ClPA (A = C14H10, anthracene) as a formal source of
phosphorus­(I) in its reaction with Na­[NV­(N­[tBu]­Ar)3] (Na­[4]) to yield
trimeric cyclo-triphosphane [PNV­(N­[tBu]­Ar)3]3 (3) with a core composed
exclusively of phosphorus and nitrogen. In the presence of NapS2 (peri-1,8-naphthalene disulfide), NapS2P-NV­(N­[tBu]­Ar)3 (6) is instead generated in 80% yield, suggesting trapping
of transient 1. Upon mild heating, 3 readily
fragments into dimeric [PNV­(N­[tBu]­Ar)3]2 (2), while in the presence of bis­(trimethyl­silyl)­acetylene
or cis-4-octene, the respective phosphirene (Ar­[tBu]­N)3­VN-PC2­(SiMe3)2 (7) or phosphirane (Ar­[tBu]­N)3­VN-P­(C8H16) (8) compounds are generated. Kinetic data were found
to be consistent with unimolecular decay of 3, and [2+1]-cycloaddition
with radical clocks ruled out a triplet intermediate, consistent with
intermediate 1 reacting as a singlet phosphin­idene.
In addition, both 7 and 8 were shown to
reversibly exchange cis-4-octene and bis­(trimethyl­silyl)­acetylene,
serving as formal sources of 1, a reactivity manifold
traditionally reserved for transition metals.