Arylphosphanide Complexes of the Heavy Alkaline Earth Metals Calcium, Strontium and Barium of the Formula (thf)_nM[P(R)Aryl]₂

Abstract

The metathesis reaction of CaI 2 with KPPh 2 in THF yields (thf) 4 Ca(PPh 2 ) 2 (1). A metallation of HPPh 2 with alkaline earth metals succeeds with strontium and barium and gives (thf) 4 Sr(PPh 2 ) 2 (2) and (thf) 5 Ba(PPh 2 ) 2 (3). From crystal structure determinations of 1 and 2 Ca-P and Sr-P bond lengths of 298.65(6) and 314.29(9) pm, respectively, were obtained. Extremely large Ba-P distances of 332.8(2) and 334.5(2) pm were found for 3. In order to investigate the influence of the bulkiness of the phosphanides on the molecular structure, (thf) 4 Ba[P(Mes) 2 ] 2 (4) and * Prof. Dr. M. Westerhausen Inst. f. Anorg. u. Analyt. 2025(thf) 2 Ba[P(Et)Ph] 2 (5) were prepared in a similar manner. Derivative 4 is monomeric with Ba-P distances of 318.72(9) pm, whereas 5 crystallizes as a one-dimensional polymer with bridging ethyl-(phenyl)phosphanide groups with Ba-P bond lengths between 324.8(1) and 336.0(1) pm. 1 H NMR (200 MHz): δ 1.72 (thf), 3.58 (thf), 6.55 (2H, t, 3 J H,H ϭ 7.2 Hz, p-CH), 6.80 (4H, t, 3 J H,H ϭ 7.4 Hz, m-CH), 7.35 (4H, dt, 4 J H,H ϭ 1.2 Hz, 3 J H,H ϭ 7.3 Hz, o-CH). 13 C{ 1 H} NMR (50 MHz): δ 26.3 (thf), 68.2 (thf), 120.8 (p-C), 127.7 (m-C, 3 J C,P ϭ 5.9 Hz), 130.9 (o-C, 2 J C,P ϭ 17.1 Hz), 153.4 (i-C, 1 J C,P ϭ 37.3 Hz). 31 P{ 1 H} NMR (81 MHz): δ Ϫ9.8 (s). MS (DEI, m/z): 52 (58 %), 78 ([C 6 H 6 ] ϩ , 100 %), 107 ([PhP Ϫ H] ϩ ,72 %), 152 ([Ph 2 Ϫ 2H] ϩ , 23 %), 183 ([Ph 2 P Ϫ 2H] ϩ , 59 %), 201 ([Ph 2 PO] ϩ , 36 %), 262 ([Ph 3 P] ϩ , 15 %), 277 ([Ph 3 PO Ϫ H] ϩ , 19 %), 370 ([Ph 2 P-PPh 2 ] ϩ , 6 %). IR (Nujol, KBr, cm Ϫ1 ): 3055 m, 1574 m, 1435 s, 1068 vw, 1025 w, 888 w, 694 vs, 502 vw, 468 vw. Synthesis of (thf) 5 Ba(PPh 2 ) 2 (3): Prepared according to Method B from (thf) 5 BaI 2 (1.98 g, 2.63 mmol) in THF (20 ml) and KPPh 2 solution (0.5 M, 10.54 ml, 5.27 mmol). 1.88 g (2.12 mmol, 81 %) pyrophoric yellow thin needles were obtained at Ϫ25°C. Decomposition above 100°C. Elemental analysis (C 32 H 36 BaP 2 O 2 , 651.90): calc.: C 58.96, H 5.57; found C 52.26, H 4.34 %.

Coordination Behavior and Coligand‐Dependent cis/trans Isomerism of Calcium Bis(diphenylphosphanides)

“…The metathesis reaction of KPPh 2 with CaI 2 in THF yields [(THF) 4 Ca(PPh 2 ) 2 ] (1), [4,5] which can be recrystallized after the removal of insoluble potassium iodide (Scheme 1). A careful investigation of the crystal shape showed two crystal morphologies, namely, cubic blocks and rod-shaped crystals.…”

“…[1] THF is an ideal solvent because it is a strong base thus ensuring the solubility of calcium diiodide as [(THF) 4 CaI 2 ], [2,3] although the nearly quantitative precipitation of KI drives the metathesis reaction completely in favor of calcium bis(phosphanide). This metathetical approach gave pure [(THF) 4 Ca(PPh 2 ) 2 ], [4,5] which proved to be a valuable catalyst in hydrophosphanylation reactions of alkynes.…”

“…This metathetical approach gave pure [(THF) 4 Ca(PPh 2 ) 2 ], [4,5] which proved to be a valuable catalyst in hydrophosphanylation reactions of alkynes. [6,7] Nevertheless, with catalytic amounts of [(THF) 4 Ca(PPh 2 ) 2 ], reactions of HPPh 2 with substituted butadiynes gave various regio-and stereoisomers. The resulting C=C double bonds remained inactive during this procedure.…”

“…Therefore, a trans arrangement of the phosphanide ligands in calcium bis(phosphanides) can be expected because this arrangement also minimizes electrostatic repulsion between the anions. This rule seems to be quite general because [(THF) 4 Ca-(PPh 2 ) 2 ], [4,5] [(THF) 4 Ca{P(H)SiiPr 3 } 2 ], [10] and [(THF) 4 Ca-{P(SiMe 3 ) 2 } 2 ]…”

“…[14] Similar trends are valid for unsolvated halides [15] and hydrides [16] with CaF 2 being bent whereas the heavier halides show linear CaX 2 molecules in contrast to bent BaX 2 . The solvation of CaI 2 (which shows a linear geometry if unsolvated) with mono-dentate Lewis bases L, such as ethers, yields [(L) 4 CaI 2 ] with a transoid arrangement of the iodide anions. [2,3,17] The addition of tetramethylethylenediamine [1,2-bis(dimethylamino)ethane, tmeda] leads to trans-[(tmeda) 2 CaI 2 ], however, tetradentate hexamethyltriethylenetetramine (hmteta) enforces a cis arrangement of the CaI 2 unit.…”