Stefano Seniori Costantini

Stabilization of the tautomers HP(OH)2 and P(OH)3 of hypophosphorous and phosphorous acids as ligands

Treatment of [CpRu(PPh(3))(2)Cl] 1 with the stoichiometric amount of H(3)PO(2) or H(3)PO(3) in the presence of chloride scavengers (AgCF(3)SO(3) or TlPF(6)) yields compounds of formula [CpRu(PPh(3))(2)(HP(OH)(2))]Y (Y = CF(3)SO(3) 2a or PF(6) 2b) and [CpRu(PPh(3))(2)(P(OH)(3))]Y (Y = CF(3)SO(3) 3aor PF(6) 3b) which contain, respectively, the HP(OH)(2) and P(OH)(3) tautomers of hypophosphorous and phosphorous acids bound to ruthenium through the phosphorus atom. The triflate derivatives 2a and 3a react further with hypophosphorous or phosphorous acids to yield, respectively, the complexes [CpRu(PPh(3))(HP(OH)(2))(2)]CF(3)SO(3) 4 and [CpRu(PPh(3))(P(OH)(3))(2)]CF(3)SO(3) 5 which are formed by substitution of one molecule of the acid for a coordinated triphenylphosphine molecule. The compounds 2 and 3 are quite stable in the solid state and in solutions of common organic solvents, but the hexafluorophosphate derivatives undergo easy transformations in CH(2)Cl(2): the hypophosphorous acid complex 2b yields the compound [CpRu(PPh(3))(2)(HP(OH)(2))]PF(2)O(2) 6, whose difluorophosphate anion originates from hydrolysis of PF(6)(-); the phosphorous acid complex 3b yields the compound [CpRu(PPh(3))(2)(PF(OH)(2))]PF(2)O(2) 7, which is produced by hydrolysis of hexafluorophosphate and substitution of a fluorine for an OH group of the coordinated acid molecule. All the compounds have been characterized by elemental analyses and NMR measurements. The crystal structures of 2a, 3a and 7 have been determined by X-ray diffraction methods.

Controlling the Activation of White Phosphorus: Formation of Phosphorous Acid and Ruthenium‐Coordinated 1‐Hydroxytriphosphane by Hydrolysis of Doubly Metalated P4

The reactivity of white phosphorus with transition-metal compounds is a mature field of inorganic and organometallic chemistry that has been extensively investigated in the past few decades. Research in this field has led to the synthesis of an amazing variety of transition-metal complexes containing Pn units originating from either the coupling or the degradation of the cage molecule(s) as well as from the recombination of smaller fragments into polyatomic aggregates. These compounds often contain species with unique geometric and electronic properties which, apart from exhibiting a rich and intriguing chemistry, have found interest either as building blocks for the construction of networks of monoand polydimensional inorganic structures or as phosphorustransfer agents towards inorganic and organic molecules. The recent activation of white phosphorus with either heterocyclic carbenes or highly nucleophilic main group compounds has led to new opportunities in this area, especially by allowing the partial degradation of the molecule and its functionalization by insertion of organic fragments into the assembled polyphosphorus units without the involvement of a transition metal. Previous work from our group has highlighted the utility of {CpRuL2} moieties (Cp R =C5H5, C5Me5; L= phosphane) for coordinating the intact P4 molecule in reactions that yield stable monoor dinuclear cationic complexes [{CpRuL2}n(h -P4)] n+ (n= 1, 2). Furthermore, these monoor bimetallic compounds, which are easily obtained in gram amounts, have proved to be useful for investigating the reactivity of coordinated P4 under mild conditions. For example, we have found that the reactivity of the coordinated P4 molecule in the cyclopentadienyl derivatives is spectacularly modified with respect to that of the free molecule as it readily undergoes quantitative disproportionation with water at room temperature. Thus, addition of excess water (100 equivalents) to one equivalent of [CpRuL2(h -P4)](CF3SO3) (1) or [{CpRuL2}2(m,h -P4)](CF3SO3)2 (2) in THF hydrolyzes the coordinated P4 ligand in a few hours to yield a mixture of phosphine (PH3), diphosphane (P2H4), and the phosphorus oxyacids H3PO2 and H3PO3 in ratios that depend strongly on the hapticity of the P4 molecule (h 1 vs. m,h). The hydrogenated molecules are stabilized by coordination to {CpRu(PPh3)2} fragment(s), [8b,c,9] whereas the oxo derivatives are obtained as either free molecules or coordinate to ruthenium after tautomerization to the pyramidal species PH(OH)2 and P(OH)3, respectively. [10] The above products, which contain one or two phosphorus atoms from the parent P4 molecule, are clearly the thermodynamic sinks in the degradation of P4, which appears to follow aspecific pathways. Herein we report further breakthroughs in this reaction and show that the reactivity of coordinated P4 is a modular process which, surprisingly, is strongly dependent on the amount of water used for the hydrolysis reaction. In particular, we demonstrate that rapid quenching of the hydrolysis of the dinuclear derivative 2 with a large excess of water affords only phosphorous acid (H3PO3) and a new bimetallic compound containing the previously unknown 1hydroxytriphosphane molecule, which is stabilized as a bridging ligand between two {CpRu(PPh3)2} fragments (Scheme 1). The formation of this molecule, besides its intrinsic interest due to the fact that it has never been observed previously either in the free state or as a ligand, gives important hints regarding the initial step of the hydrolytic degradation of coordinated P4 and pinpoints the existence of a selective disproportionation of P4 that differs from its well-known alkaline hydrolysis, which gives only PH3 and hypophosphorous acid (H3PO2). The addition of 500 equivalents of water to one equivalent of 2 in THF is a simple process that leads to the formation of one equivalent of H3PO3 and one equivalent of the new complex [{CpRu(PPh3)2}2{m ,h-PH(OH)PHPH2}](CF3SO3)2 (3) within a few minutes ( P NMR monitoring). Work-up of this solution gave 3 in excellent yield, and recrystallization from CHCl3/n-hexane provided yellow crystals suitable for X-ray analysis. The diruthenium cation in 3 contains the previously unknown molecule PH(OH)PHPH2, which bridges two {CpRu(PPh3)2} moieties through the phosphorus atoms of the PH(OH) and PH2 end-groups. These two groups are affected by twofold positional disorder in the solid-state [*] Prof. Dr. M. Di Vaira, Dr. S. Seniori Costantini, Prof. Dr. P. Stoppioni Dipartimento di Chimica, Universit& di Firenze via della Lastruccia,3, 50019 Sesto Fiorentino, Firenze, (Italy) Fax: (+39)0554573385 E-mail: piero.stoppioni@unifi.it

Getting a clue to the hydrolytic activation of white phosphorus: the generation and stabilization of P(OH)2PHPHPH(OH) at ruthenium centers.

The bimetallic compound [{CpRu(PPh(3))(2)}(2)(mu,eta(1:1)-P(4))][CF(3)SO(3)](2), in which the tetrahedral P(4) is bound to two CpRu(PPh(3))(2) fragments, slowly reacts under mild conditions with a moderate excess of water (1:20) to yield a mixture of compounds. Among the hydrolysis products, the new, remarkably stable complexes [{CpRu(PPh(3))}{CpRu(PPh(3))(2)}{mu(1,4:3),eta(2:1)-P(OH)(2)PHPHPH(OH)}](CF(3)SO(3))(2) (2) and [{CpRu(PPh(3))(2)}{CpRu(PPh(3)){P(OH)(3))}(mu,eta(1:1)-P(2)H(4))](CF(3)SO(3))(2) (3) have been isolated. In the former, the previously unknown 1,1,4-tris(hydroxy)tetraphosphane molecule, P(OH)(2)PHPHPH(OH), is 1,4- and, respectively, 3-coordinated to the CpRu(PPh(3)) and the CpRu(PPh(3))(2) moieties; in the latter, the diphosphane P(2)H(4) is stabilized through coordination to two different metal fragments. All of the compounds were characterized by elemental analyses and IR and NMR spectroscopy. The crystal structure of 2 was determined by X-ray analysis. The formation of the hydroxytetraphosphane, containing the tetraphosphorus entity, provides a clue to the hydrolytic activation of the P(4) molecule.

Iodine Activation of Coordinated White Phosphorus: Formation and Transformation of 1,3‐Dihydride‐2‐iodidecyclotetraphosphane

Double stabilization: Previously unknown polyphosphorus compounds are obtained by activation of white phosphorus (P(4)) coordinated between two CpRu(PPh(3))(2) moieties with iodine, and subsequent hydrolysis. The polyphosphorus compounds (P(4) H(2) I, P(4) H(2), P(3) H(5); see scheme, Cp=cyclopentadienyl) are all stabilized by coordination to two ruthenium centers.