Benzonitrile Adducts of Terminal Diarylphosphido Complexes: Preparative Sources of “Ru═PR₂”

Abstract

Dehydrohalogenation of secondary diarylphosphine ruthenium complexes in the presence of benzonitrile yields stable, isolable nitrile adducts of the formula [Ru(η 5indenyl)(PAr 2 )(NCPh)(PPh 3 )], in which the terminal phosphido ligand is pyramidal at P and contains a stereochemically active lone pair. Unlike the analogous carbonyl adducts [Ru(η 5 -indenyl)(PAr 2 )(CO)(PPh 3 )], these benzonitrile complexes behave as masked sources of the highly reactive planar phosphido complexes [Ru(η 5 -indenyl)(PAr 2 )(PPh 3 )], which contain a RuPAr 2 π bond. This is illustrated by the addition (or cycloaddition) reactions of the benzonitrile adducts with dihydrogen, methyl iodide, and 1-hexene, as well as their thermal decomposition via orthometalation of the PPh 3 ligand. Enthalpies of CO vs NCPh dissociation from the [Ru(η 5indenyl)(PR 2 )(PPh 3 )] fragments (R = alkyl, aryl) have been calculated, as has the trajectory of addition of H 2 to the model planar phosphido complex [Ru(η 5 -indenyl)(PMe 2 )(PMe 3 )]. The latter study shows the intermediacy of an η 2 -H 2 adduct, [Ru(η 5 -indenyl)(PAr 2 )(η 2 -H 2 )(PPh 3 )], in the formation of [RuH(η 5 -indenyl)(HPMe 2 )(PMe 3 )], a further indication of the importance of the variable binding modes of the terminal phosphido ligand in this system.

Heterolytic Cleavage of Dihydrogen by an Iron(II) PNP Pincer Complex via Metal–Ligand Cooperation

“…donors) to leave a hydride ligand on the metal center has been extensively studied in recent years (Scheme 1). 7 …”

Addition of H2 Across a Cobalt–Phosphorus Bond

“…Both stoichiometric and catalytic reactions involving the addition of s bonds across metal-element bonds (element = N, O, C, B, S) have become increasingly prevalent. [25][26][27][28][29][30][31][32] In av ery recent paper by Gudat and coworkers,ametal phosphenium complex, (uNHP Dipp )Mn(CO) 4 (where NHP R indicates amonodentate NHP + cation with N-Rs ubstituents," u" indicates an unsaturated backbone,a nd Dipp = 2,6-diisopropylphenyl), was shown to be an active catalyst for the catalytic dehydrogenation of NH 3 BH 3 . [21][22][23][24] Related examples of metalligand cooperativity involving phosphorus are far less common.…”

“…[25][26][27][28][29][30][31][32] In av ery recent paper by Gudat and coworkers,ametal phosphenium complex, (uNHP Dipp )Mn(CO) 4 (where NHP R indicates amonodentate NHP + cation with N-Rs ubstituents," u" indicates an unsaturated backbone,a nd Dipp = 2,6-diisopropylphenyl), was shown to be an active catalyst for the catalytic dehydrogenation of NH 3 BH 3 . [28][29][30][31][32] Extension of the metal-ligand cooperativity observed for amide/amine systems to phosphide/phosphines poses as ignificant challenge,b ut may result in more reactive systems since P À H bonds are generally weaker and more acidic than N À Hbonds, and because metal phosphides are more nucleophilic than their metal amide congeners. [33] In fact, there are only af ew examples of H 2 addition across aM ÀPb ond.…”

Reactivity of Ruthenium Phosphido Species Generated through the Deprotonation of a Tripodal Phosphine Ligand and Implications for Hydrophosphination

“…The Rosenberg and Peters groups have both shown that phosphidos are able to deprotonate and orthometalate a phenyl substituent of a cisphosphine ligand on coordinatively unsaturated ruthenium(II) complexes. 17,28,36 This, followed by deprotonation of the resulting phosphine and reductive elimination of the alkyl and phosphido functionalities, could form the 1,2-diphosphinobenzene linkage. In order to reduce the unsaturated backbone from the dppen ligand, on the other hand, the hydrogen atoms would need to come from the activated Cp* methyl group and the aromatic o-C−H bond.…”

“…Despite the metal−phosphorus double bond, planar phosphidos have reactivity similar to that of terminal phosphidos in that they are very basic and nucleophilic; they have even been reported to deprotonate phenyl groups. 17,28,36 Phosphido ligands are especially important in the latetransition-metal-catalyzed hydrophosphination of unsaturated substrates, as conventional organometallic catalytic mechanisms involve the insertion of an alkene or alkyne into the M−P bond of a phosphido intermediate. 22−26,37−59 A typical organometallic mechanism for alkene hydrophosphination involves oxidative addition of a primary or secondary phosphine to an electron-rich metal center followed by coordination of the olefin substrate and subsequent insertion to form a P−C bond (Scheme 1).…”