Highly Selective Chromium(0)‐Mediated Insertion of Nitriles into a Nonpolar P–P Bond of a Substituted Hexahydro‐1,4‐diaza‐2,3,5,6‐tetraphosphorine

Abstract

The cleavage of P-P σ bonds has long been a subject of interest and is investigated widely. P-P bonds can be cleaved homolytically to yield phosphinyl radicals, which can be persistent and stable for long periods or undergo further reactions. P-P bonds that exhibit polarization owing to different substitution can be opened heterolytically. Furthermore, it is possible to activate them through metal interactions. Both processes can [a] 3009 Scheme 2. Different ways to prepare 2 and the competitive reaction to form 3 (pip = piperidine).Scheme 3. The selective insertion of acetonitrile (left) or benzonitrile (right) into one (P-P) bond of the ligand leads to 4 or 5, respectively.

Unusual Reactivity of cyclo‐(P5Ph5): Oxidative Addition at a Group 6 Metal Carbonyl and Insertion of Acetonitrile into a P–P Bond

“…The small M–P–M bond angles [75.06(2)–77.95(6)°] for the complexes are similar to literature values,, , as are the large P–M–P bond angles [102.12(7)–104.22(3)°] , , , . The P(2)–P(3)–P(4) [103.09(4)–106.29(3)°] bond angles fall within the range [94.1(2)–107.2(2)°] for cyclo ‐(Ph 5 P 5 ) and similar compounds like P[P(S)Me 2 ] 3 …”

“…The coordination sphere for each metal atom is completed by three terminal carbonyl ligands and one coordinating phosphorus atom (P3 for M2 and or P4 for M1) of the novel ligand. The M1–M2 distances (Table and Table S2, ESI) are 2.893(1) Å for 1a , 3.0253(2) Å for 1b , 3.0279(2) Å for 1c and 3.0279(2) Å for 2c , and fall within the range of metal–metal bonds for other M 2 P 2 (CO) x units in similar Cr [2.8925(8)–2.949(1) Å],, Mo [3.022(4)–3.057(6) Å], and W [3.017(2)–3.078(5) Å] complexes. The bridging M–P bonds fall in the ranges 2.297(2)–2.337(2) Å ( 1a ), 2.4335(5)–2.4668(5) Å ( 1b ), 2.4363(9)–2.4675(9) Å ( 1c ) and 2.4348(8)–2.4949(9) Å ( 2c ).…”

“…S1–S3, ESI) contain an M–M unit bridged by the two terminal phosphanido groups of the novel ligand, (PPh‐PPh‐PPh‐PPh‐CMe=N‐PPh) 2– , with an all‐ trans arrangement of the phenyl groups. Although heteroleptic dinuclear bis‐phosphanido‐bridged complexes with M 2 P 2 units are known,, these are the first examples in which the bridging phosphorus atoms are linked to a chain of phosphorus atoms. Both metal atoms are in the formal oxidation state +I and have a distorted octahedral geometry with a planar M 2 P 2 unit.…”

“…Furthermore, P–P bonds can be cleaved homolytically or, when polarised, especially when activated through coordination to a metal atom, heterolytically , . Both of these processes can result in the insertion of unsaturated small molecules into the homonuclear σ‐bonds . The insertion of small molecules into homo‐ and heteronuclear element–element (E–E) single bonds has been the subject of intense research, since this important transformation can be of significance in catalytic processes.…”

“…Wolf et al reported the reversible insertion of the C=S or C=N bond of phenyl isothiocyanate into a P–P bond of [{CpNi(IMes)} 2 (µ‐η 1 :η 1 ‐P 4 )] {IMes = 1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene} . Furthermore, a highly selective metal‐mediated insertion of nitriles into a nonpolar P–P bond of a substituted hexahydro‐1,4‐diaza‐2,3,5,6‐tetraphosphorine has been reported by Rosenthal et al Recent studies by Manners et al have shown that nitrile or isocyanide insertion into P–P bonds of phosphorus homocycles takes place easily for polarized molecules, such as { cyclo ‐(P 3 t Bu 3 )Me} + and { cyclo ‐(P 4 t Bu 4 )Me} + , but does not proceed with the neutral molecules, cyclo ‐(P 3 t Bu 3 ) and cyclo ‐(P 4 t Bu 4 ) . In addition, stoichiometric and acid‐catalyzed insertion of nitriles into a P–P bond of cyclo ‐(P 3 t Bu 3 ) resulted in the first free 1‐aza‐2,3,4‐triphospholenes …”