Ruthenium‐Stabilized Low‐Coordinate Phosphorus Atoms: Structural Evidence for Monomeric Metaphosphonate

Abstract

The metaphosphate anion has attracted steady interest since 1955 [1] in connection with wide applications in phosphorylation reactions.[2] It has relevance in biochemistry in particular with respect to ATP hydrolysis.[3] However, despite considerable efforts, monomeric metaphosphates and other dioxophosphoranes are only known as transient species in solution and their existence can be inferred from trapping experiments. [2][3][4] Their high reactivity arises from the powerful electrophilic character at the phosphorus center. Several approaches have been tested to stabilize these highly reactive species. Kinetic stabilization by steric protection [5] proved to be ineffective for dioxophosphorane and led to products that resulted from the insertion of the PO 2 moiety in a neighboring group.[6] The electrophilicity and the tendency to expand the valence shell were exploited for their stabilization as Lewis salts. This strategy allowed only spectroscopic characterization by 31 P NMR in a few cases. [7] Thus, the chemistry of dioxophosphorane suffers from a paucity of information and new approaches to stabilize and enable deeper investigation are highly desirable. This work describes the first isolation and full characterization, including X-ray structural analysis, of stabilized metaphosphonate.We have developed a novel and successful route to ruthenium-stabilized monomeric metaphosphonate by oxidation of a nucleophilic terminal phosphinidene complex of ruthenium. As recently described by Lammerstma and coworkers, the terminal phosphinidene ruthenium complexes [(h 6 -p-cymene)Ru(PR 3 )(PMes*)] (3 a: R = Cy, 3 b: R = Ph [8] ) are formed as dark green solids by the reaction of the primary phosphane complex [(h 6 -p-cymene)RuCl 2 (PH 2 Mes*)](1; pcymene = 4-methyl-iso-propylbenzene; Mes* = 2,4,6-tri-tertbutylphenyl) with two equivalents of 1,8-diazabicyclo[5-4-0]undec-7-ene (DBU) in the presence of PR 3 as a stabilizing ligand (R = Ph, Cy).[8] Alternatively, treatment of [(h 6 -pcymene)RuCl 2 (PR 3 )] (2 a: R = Cy, 2 b: R = Ph) and PH 2 Mes* with DBU affords 3 in high yields (Scheme 1).

Nucleophilic behaviour of dioxo- and thiooxophosphorane complexes [MoCp(CO)2{E,P-EP(O)(2,4,6-C6H2tBu3)}]−(E = O, S)

“…This is not unusual in the chemistry of silicon, and might be associated with some participation of the lone electron pairs at oxygen in  bonding along the POSi chain, while at the same time alleviating the steric pressure around the P atom. For instance, in the cis and trans isomers of the complex [PdCl 2 {P(OSiMe 3 ) 3 23 Spectroscopic data in solution for compounds 9 to 11 (Table 1 and Experimental Section) are fully consistent with the structure found for 9 in the crystal, and are comparable to those of the phosphonothiolate complexes 6 and 7, then deserving no detailed analysis. We just note that the CO stretching frequencies of these complexes broadly reflect the expected trend based on the electron withdrawing power of the electrophile being attached to the O atom of the phosphorus ligand, by following the sequence 6 (CH 3 ) > 9 (SiMe 3 ) >> 11 (ZrCp 2 Cl) > 10 (SnMe 3 ).…”

“…Compound 3 reacts readily with the relatively hard electrophiles SiMe 3 6 (R = Ph, Me; THT = SC 4 H 8 ) yielded similar derivatives, as judged from the corresponding IR and NMR spectra, but these products were quite unstable and could not be properly isolated and characterized.…”

“…However, the coordination chemistry of these molecules is virtually unknown, with just one example described for a dioxophosphorane complex. 3 In a preliminary study we found that the anionic oxophosphinidene complex (H- …”

“…However, the coordination chemistry of these molecules is virtually unknown, with just one example described for a dioxophosphorane complex. 3 In a preliminary study we found that the anionic oxophosphinidene complex (H-(1), (R* = 2,4,6-C 6 H 2 t Bu 3 ; Cp= and thiooxophosphorane (H-DBU)[MoCp(CO) 2 {S,P-SP(O)R*}] (3) derivatives (Scheme 1). 4 Because of the negative charge of the latter complexes, the acid-base chemistry of their phosphorus ligands is reversed, so they can now behave as nucleophiles.…”

Phosphines and Related Tervalent Phosphorus Systems

“…771 Although strictly outside the remit of this chapter, it is appropriate to note continued activity in the chemistry of s 3 l 5 -p p -bonded phosphorus compounds that do not possess a lone pair of electrons at phosphorus. A monomeric metaphosphonate species (262, X¼O) has been stabilised by coordination (via the P¼O bond), 773 and Harger's group has provided evidence of the intermediacy of metathiophosphonates (262, X¼S) in the reactions of phosphonamidothioic acids with alcohols. 774 The cation (263) has been stabilised by coordination at phosphorus with 4-dimethylaminopyridine 775 and the reactivity of bis(methylene)phosphoranes (264) …”