Recent plant diversity changes on Europe's mountain summits.

In mountainous regions, climate warming is expected to shift species' ranges to higher altitudes. Evidence for such shifts is still mostly from revisitations of historical sites. We present recent (2001 to 2008) changes in vascular plant species richness observed in a standardized monitoring network across Europe's major mountain ranges. Species have moved upslope on average. However, these shifts had opposite effects on the summit floras' species richness in boreal-temperate mountain regions (+3.9 species on average) and Mediterranean mountain regions (-1.4 species), probably because recent climatic trends have decreased the availability of water in the European south. Because Mediterranean mountains are particularly rich in endemic species, a continuation of these trends might shrink the European mountain flora, despite an average increase in summit species richness across the region.

Reactions of a phosphinoaldehyde with Pd(II), Rh(I), and Ir(I) precursors, including the formation of complexes containing a P,OH-chelated phosphinohemiacetal ligand: a new bonding mode.

The complexes trans-PdCl(2)[eta(1)-P-(Ph(2)P)CH(Ph)CH(Me)CH(OMe)(2)](2) (1) and M(H)Cl[eta(2)-P,OH-(Ph(2)P)CH(Ph)CH(Me)CH(OH)OMe][eta(2)-P,C(O)-(Ph(2)P)CH(Ph)CH(Me)C(O)], M = Rh (3) and Ir (4), are synthesized by reacting the phosphinoaldehyde [3-(diphenylphosphino)-3-phenyl-2-methyl]propionaldehyde [(Ph(2)P)(2)CH(Ph)CH(Me)CHO] with trans-PdCl(2)(PhCN)(2), [RhCl(COD)](2), and [IrCl(COD)](2), respectively, in MeOH; trans-PdCl(2)[eta(1)-P-(Ph(2)P)CH(Ph)CH(Me)CHO](2) (2) is isolated from the same reaction in CH(2)Cl(2). One diastereomer of each of the complexes 1, 3 x MeOH, and 4 x MeOH was characterized by X-ray analysis. The stereochemistry of such complexes in the solid state and in solution (MeOH and CH(2)Cl(2)) is discussed. In CD(2)Cl(2), NMR data suggest that the coordinated hemiacetal moiety of 3 (but not 4) undergoes reversible loss of MeOH; this process is associated with equilibria between various diastereomers of 3 that were investigated by (31)P{(1)H}, (13)C{(1)H}, (1)H, (1)H{(31)P}, and HSQC and HMBC (1)H/(31)P{(1)H} and (1)H/(13)C{(1)H} NMR spectroscopies. Complexes 3 and 4 reveal a new chelate bonding mode via a P atom and the hydroxyl O atom of a hemiacetal. Solvent-dependent stereochemical changes within solution species imply that such chiral phosphinoaldehydes are not likely to be useful ligands for applications in asymmetric catalysis, although conditions are suggested for testing the complexes as potential precursors for nonasymmetric catalytic processes.

Reactions of tertiary phosphines with alcohols in aqueous media.

The phosphines R(2)R'P [R = R' = Me, Et, (n)Pr, (i)Pr, (CH(2))(3)OH; Me(2)PhP and MePh(2)P] react with 2- or 4-hydroxybenzyl alcohols, including "lignin-type" vanillyl, syringyl, and alpha-methylvanillyl alcohols, in a 1:1 ratio in aqueous media, to give zwitterionic phosphobetaine products; these on treatment with aq HCl form the corresponding phosphonium chlorides in good to excellent yields. The syringyl derivative [3,5-(OMe)(2)-4-OH-C(6)H(2)CH(2)PEt(3)]Cl was structurally characterized by X-ray analysis. Kinetically, the reactivity of the benzyl alcohols, studied with the water-soluble [HO(CH(2))(3)](3)P, decreases with substituents in the order 2-hydroxy > 4-hydroxy > vanillyl > syringyl > alpha-methylvanillyl, while 3-hydroxybenzyl alcohol is unreactive; the trend is consistent with reactivity requiring the presence of an ortho- or para-OH substituent in the aromatic ring of the alcohol, and that the reactions proceed via a carbocation species stabilized as a quinone methide. Triethylphosphine reacts with coniferyl alcohol at the C=C moiety to give a zwitterionic intermediate that is again converted by aq HCl to a phosphonium chloride; no reaction was observed with cinnamyl alcohol. The effect on a phenolic pK(a) by incorporation of a phosphonium substituent is also measured.

New tertiary phosphines from cinnamaldehydes and diphenylphosphine.

A 1:1 hydrophosphination of the olefinic bond of cinnamaldehyde (and substituted ones) with Ph2PH, under argon using neat reagents, gives quantitative formation of the new tertiary phosphines Ph2PCH(Ar)CH2CHO (2) as racemic mixtures (Ar = Ph, p-tol, and p-OMe-C6H4). alpha-Methylcinnamaldehyde similarly affords Ph2PCH(Ph)CH(Me)CHO, but as a mixture of diastereomers with predominantly S,S- and R,R-chirality [diastereomeric ratio (dr) approximately 20]. In a 2:1 reaction of Ph2PH with cinnamaldehyde, hydrophosphination of both the C=C and C=O bonds takes place to give the diphosphine derivative Ph2PCH(Ph)CH2CH(OH)PPh2 (3) as a diastereomeric mixture with dr approximately 2.3. In most organic solvents, the hydrophosphination of the C=O group is reversible, leading to a dynamic equilibrium between 3 and 2, but 3 is stable in coordinating solvents such as DMSO, DMF, and pyridine. X-ray analysis of a P,P-chelated PdCl2(3) complex, formed from trans-PdCl2(PhCN)2 and 3 in MeOH, reveals that the S,S/R,R-enantiomers are favored.

Interaction of tertiary phosphines with lignin-type, alpha,beta-unsaturated aldehydes in water.

To learn more about the bleaching action of pulps by (hydroxymethyl)phosphines, lignin chromophores, such as the alpha,beta-unsaturated aromatic aldehydes, sinapaldehyde, coniferylaldehyde, and coumaraldehyde, were reacted with the tertiary phosphines R2R'P [R = R' = Me, Et, (CH2)3OH, iPr, cyclo-C6H11, (CH2)2CN; R = Me or Et, R' = Ph; R = Ph, R' = Me, m-NaSO3-C6H4] in water at room temperature under argon. In all cases, initial nucleophilic attack of the phosphine occurs at the activated C=C bond to form a zwitterionic monophosphonium species. With the phosphines PR3 [R = Me, Et, (CH2)3OH] and with R2R'P (R = Me or Et, R' = Ph), the zwitterion undergoes self-condensation to give a bisphosphonium zwitterion that can react with aqueous HCl to form the corresponding dichloride salts (as a mixture of R,R- and S,S-enantiomers); X-ray structures are presented for the bisphosphonium chlorides synthesized from the Et3P and Me3P reactions with sinapaldehyde. With the more bulky phosphines, iPr3P, MePPh2, (cyclo-C6H11)3P, and Na[Ph2P(m-SO3-C6H4)], only an equilibrium of the monophosphonium zwitterion with the reactant aldehyde is observed. The weakly nucleophilic [NC(CH2)2]3P does not react with sinapaldehyde. An analysis of some exceptional 1H NMR data within the prochiral phosphorus centers of the bisphosphonium chlorides is also presented.

Chemistry and stereochemistry of the interaction of the water-soluble phosphine [HO(CH2)3]3P with cinnamaldehyde in aqueous media.

To learn more about the bleaching action of pulps by (hydroxymethyl)phosphines, cinnamaldehyde was reacted with tris(3-hydroxypropyl)phosphine, [HO(CH2)3]3P (THPP), in aqueous solution at room temperature under argon. Self-condensation of the aldehyde into two isomeric products, 2-benzyl-5-phenyl-pent-2,4-dienal and 5-phenyl-2-(phenylmethylene)-4-pentenal, is observed; this implies initial nucleophilic attack of the phosphine at the beta-carbon of the alpha,beta-unsaturated aldehyde. Reaction in D2O gives the same products in which all but the phenyl and CHO protons are replaced by deuterons. NMR studies are consistent with carbanion formation and subsequent condensation of two phosphonium-containing aldehyde moieties to generate the products with concomitant elimination of phosphine oxide. In D2O in the presence of HCl, THPP reversibly attacks the aldehyde-C atom to form the (alpha-hydroxy)phosphonium derivative [PhCH=C(H)CH(OD)PR3]Cl (where R=(CH2)3OD), which slowly converts into the deuterated bisphosphonium salt [R3PCH(Ph)CD(H)CH(OD)PR3]Cl2 via the deuterated monophosphonium salt [R3PCH(Ph)CD(H)CHO]Cl. The phosphonium intermediates and phosphonium products in this chemistry, although having up to three chiral carbon centers, are formed with high stereoselectivity just in enantiomeric forms. In acetone-H2O (1:1 v/v), a cross-condensation of cinnamaldehyde with acetone to give 6-phenyl-3,5-hexadien-2-one is promoted by THPP via generation of OH-.

Alpha-monodeuterated benzyl alcohols and phosphobetaines from reactions of aromatic aldehydes with a water/D2O-soluble phosphine.

With the aim of learning more about the bleaching action of pulps by (hydroxymethyl)phosphines, we reacted several benzaldehydes, containing MeO, Me, OH, or halogen substituents, with tris(3-hydroxypropyl)phosphine, [HO(CH2)3]3P, in aqueous solution at 90 degrees C under argon. Effective reduction of the aldehydes to the corresponding benzyl alcohols with concomitant oxidation of the phosphine to the phosphine oxide takes place, the reaction proceeding via an initially formed phosphonium species. When the reactions are carried out in D2O, the benzyl alcohol product from 3,4-dimethoxybenzaldehyde contains one deuterium atom at the benzyl-carbon atom, consistent with the last step of the mechanism involving a carbanion intermediate. With syringaldehyde (3,5-dimethoxy-4-hydroxy-benzaldehyde), the reduction product (syringyl alcohol) is more reactive toward the phosphine than is the starting aldehyde, and a zwitterionic, phosphobetaine product is formed. In D2O, the zwitterion benzyl protons and protons of the hydroxypropyl-CH2 adjacent to the P atom undergo H/D exchange via presumed phosphorus ylide intermediates. Under the same aqueous reaction conditions, tris(3-hydroxypropyl)phosphine, [HO(CH2)3]3P (THPP), does not undergo redox reactions with aliphatic aldehydes but simply promotes a base-catalyzed self-condensation (aldol) reaction. THPP reduction of an aromatic ketone is sluggish, presumably because the carbonyl C-atom is less electrophilic than that present in an aromatic aldehyde.

New oligophosphines and (hydroxymethyl)phosphonium chlorides.

The new oligophosphines [H2P(CH2)2]2PH, [H2P(CH2)2P(H)CH2]2, and{[(H2P(CH2)2]2PCH2}2 have been made by hydrophosphination of diethyl vinylphosphonate (2) with H2P(CH2)2PH2 (1), using different ratios of 2/1, followed by LiAlH4 reduction of the phosphonate intermediates; the three phosphonate precursors were obtained as oils of varying purity (approximately 90-95%) in low (approximately 20%) to almost quantitative yield. The tri-, tetra-, and hexaphosphines were then treated with formaldehyde in the presence of hydrochloric acid to generate the corresponding water-soluble (hydroxymethyl)phosphonium chlorides {(HOCH2)3P[(CH2)2P(CH2OH)2]n(CH2)2P(CH2OH)3}Cl m (n = 1, m = 3; n = 2, m = 4) and {[(HOCH2)3P(CH2)2]2P(CH2OH)CH2}2Cl6 that were characterized by NMR spectroscopy and elemental analysis. The known (hydroxymethyl)bisphosphonium chloride [(HOCH2)3P(CH2)2]2Cl2 was similarly prepared from H2P(CH2)2PH2, and the determined crystal structure revealed strong hydrogen bonding between the chloride anions and the hydrogen atoms of the hydroxymethyl groups.