The tetrahydrofuran adducts [(thf)(4)M(PPh(2))(2)] (M = Ca, Sr) are air sensitive and can easily be oxidized by chalcogens. Metalation of diphenylphosphane oxide, diphenylphosphinic acid, and diphenyldithiophosphinic acid as well as salt metathetical approaches of the potassium salts with MI(2) allow the synthesis of [(thf)(4)Ca(OPPh(2))(2)] (1), [(dmso)(2)Ca(O(2)PPh(2))(2)] (2), [(thf)(3)Ca(O(2)PPh(2))I](2) (3), [(thf)(3)Ca(S(2)PPh(2))(2)] (4), [(thf)(2)Ca(Se(2)PPh(2))(2)] (5), [(thf)(3)Sr(S(2)PPh(2))(2)] (6), [(thf)(3)Sr(Se(2)PPh(2))(2)] (7), and [(thf)(2)Ca(O(2)PPh(2))(S(2)PPh(2))](2) (8), respectively. The diphenylphosphinite anion in 1 contains a phosphorus atom in a trigonal pyramidal environment and binds terminally via the oxygen atom to calcium. The diphenylphosphinate anions act as bridging ligands leading to polymeric structures of calcium bis(diphenylphosphinates). Therefore strong Lewis bases such as dimethylsulfoxide (dmso) are required to recrystallize this complex yielding chain-like 2. The chain structure can also be cut into smaller units by ligands which avoid bridging positions such as iodide and diphenyldithiophosphinate (3 and 8, respectively). In general, diphenyldithio- and -diselenophosphinate anions act as terminal ligands and allow the isolation of mononuclear complexes 4 to 7. In these molecules the alkaline earth metals show coordination numbers of six (5) and seven (4, 6, and 7).
The calcium-mediated addition of diphenylphosphane oxide to organic isocyanates and isothiocyanates yields N-alkyl and N-aryl substituted diphenylphosphorylformamides (E = O, R = iPr, tBu, cHex, Ph, C6H4-4-Br, C6H2-2,4,6-Me3, and Naph) and -thioformamides (E = S, R = iPr, cHex, Ph, and C6H4-4-Me), respectively, of the type Ph2P(O)–C(E)–N(H)R. All derivatives were characterized by IR and NMR spectroscopy as well as X-ray diffraction experiments. The wavenumbers of the N–H stretching modes are smaller for the thio analogues and N-aryl substituents. In the solid state all formamides and thioformamides form dimers by N–H⋯O–P hydrogen bridges. The P–CCE bonds are significantly elongated compared with the P–CPh distances.
The salt metathesis reaction of KPPh2 with CaI2 and SrI2 in THF yields the corresponding complexes [(THF)4Ae(PPh2)2] [Ae = Ca (1), Sr]. Depending on the crystallization conditions, cis‐ or trans‐[(THF)4Ca(PPh2)2] can be isolated. In solution, a fast equilibrium converts these isomers into each other leading to a single set of resonances in the NMR spectra. The THF ligands can be replaced by stronger Lewis bases, such as N‐methylimidazole (MeIm), which leads to the formation of [(MeIm)4Ae(PPh2)2] [Ae = Ca (2a), Sr (2b)]. The use of tetradentate hexamethyltriethylenetetramine (hmteta) fixes a cis configuration yielding [(hmteta)Ca(PPh2)2] (3). All compounds are very air and moisture sensitive, therefore a few crystals of the partially oxidized product [(hmteta)Ca(PPh2)(OPPh2)] (4) were also obtained.
The reaction of [(thf)4Ca(PPh2)2] (1) with diisopropyl– and dicyclohexylcarbodiimides yields the phospha(III)guanidinates [(thf)2Ca{RNC(PPh2)NR}2] with R = isopropyl (2) and cyclohexyl (3). The metathesis reaction of K{RNC(PPh2)NR} with anhydrous CaI2 also allows the synthesis of these phospha(III)guanidinate complexes 2 and 3. For 2 a cis arrangement is observed whereas 3 crystallizes as trans isomer. The phospha(III)guanidinates act as bidentate chelate bases with an average Ca–N distance of 242.5 pm. The C–P bond length between the PPh2 fragment and the 1,3–diazaallyl unit is with values above 190 pm very large. The complexes 2 and 3 show a moderate catalytic activity in hydrophosphanylation reactions of dialkylcarbodiimides with diphenylphosphane.
The hydroamination of diphenylbutadiyne with 1 equiv of the secondary amines HNRR' (R/R' = Ph/Ph, Ph/Me, and pTol/Me) in the presence of catalytic amounts of the tetrakis(amino)calciate K2[Ca{N(H)Dipp}4] (Dipp = 2,6-diisopropylphenyl) yields the corresponding 1-(diorganylamino)-1,4-diphenylbut-1-ene-3-ynes as a mixture of E/Z isomers. These tertiary alkenylamines react with diphenylphosphane to form RR'N-C(Ph)═CH-CH═C(Ph)-PPh2 [R/R' = Ph/Ph (1), Ph/Me (2), and pTol/Me (3)] in the presence of catalytic amounts of [(THF)4Ca(PPh2)2] or of the same calciate K2[Ca{N(H)Dipp}4]. Whereas the hydroamination is regio- (amino group in 1-position) but not stereoselective (formation of E and Z isomers), this second hydrofunctionalization step is regio- (phosphanyl group in 4-position) and stereoselective (only E isomers are formed), finally leading to mixtures of (E,E)- and (Z,E)-1-(diorganylamino)-1,4-diphenyl-4-(diphenylphosphanyl)buta-1,3-dienes.
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