substituents. This value differs from the Tolman cone angle
(determined by molecular modelling) by using the centre of the
H atom and the real Pt–P bond length. It is also likely to differ
due to the volume of space occupied by the phosphine being
partly determined by the coordination environment provided by
the Pt. The values obtained clearly confirm the smaller size of
ligand 4 with respect to ligand 2. It has been estimated that the
Tolman cone angle of 2 is 145°.2
The crystal structure of 6 reveals different structural features
to the other crystal structure studies of tris(dialkylamino)phos-
phines. This may suggest that the bonding observed in these
compounds is slightly more subtle than we originally supposed,
and could also be related to the exact coordination environment
of the ligand. The coordination environment provided by the Pt
complex is also likely to have an effect on the ligand structure
observed within that of complex 8. In conclusion, we have
prepared three new phosphine ligands and shown them to be
especially strong donor ligands. Studies to evaluate the potential
uses of these ligands in catalysis are now underway.
Fig. 1 Ball and stick representation of [P(N-pyrr)3]2PtCl2 6. Selected bond
lengths (Å) and angles (°): Pt–P(1) 2.246(3), Pt–P(2) 2.270(3), Pt–Cl(1)
2.398(3), Pt–Cl(2) 2.371(3); P(2)–Pt–P(1) 98.24(10), Cl(2)–Pt–Cl(1)
85.08(11).
We are grateful to the EPRSC for financial support, and the
Joint Research Equipment Initiative for an equipment grant.
Notes and references
1 C. A. Tolman, Chem Rev., 1977, 77, 313; Md. M. Rahman, H.-Y. Lie,
K. Eriks, A. Prock and W. P. Giering, Organometallics, 1989, 8, 1 and
references therein; M. F. Ernst and D. M. Roddick, Inorg. Chem., 1989,
28, 1624.
2 K. G. Molloy and J. L. Petersen, J. Am. Chem. Soc., 1995, 117, 7696.
3 M. C. Simpson and D. J. Cole-Hamilton, Coord. Chem. Rev., 1996, 155,
163 and references therein.
4 Catalytic C–H bond activation: T. Sakakura, T. Sodeyama, K. Sasaki, K.
Wada and M. Tanaka, J. Am. Chem. Soc., 1990, 112, 7221 and
references therein.
5 Hydroformylation: J. K. MacDougall, M. C. Simpson, M. J. Green and
D. J. Cole-Hamilton, J. Chem. Soc., Dalton Trans., 1996, 1161 and
references therein.
Fig. 2 Ball and stick representation of [MeP(N-pyrr)2]2PtCl2 8. Selected
bond lengths (Å) and angles (°): Pt–P(1) 2.226(2), Pt–P(2) 2.255(2), Pt–
Cl(1) 2.372(2), Pt–Cl(2) 2.391(2); P(2)–Pt–P(1) 93.37(7), Cl(1)–Pt–Cl(2)
86.14(8).
6 Pd catalysed substitutions of aryl chlorides: A. F. Littke and G. C. Fu,
J. Org. Chem., 1999, 64, 10; Angew. Chem., Int. Ed., 1999, 38, 2411;
J. P. Wolfe, R. A. Singer, B. H. Yang and S. L. Buchwald, J. Am. Chem.
Soc., 1999, 121, 9550; B. C. Hamann and J. F. Hartwig, J. Am. Chem.
Soc., 1998, 120, 7370.
7 A. H. Cowley, M. Lattman, P. M. Stricklen and J. G. Verkade, Inorg.
Chem., 1982, 21, 453; C. Romming and J. Songstad, Acta Chem. Scand.,
Ser. A., 1978, 32, 689; C. Romming and J. Songstad, Acta Chem. Scand.,
Ser. A., 1979, 33, 187; C. Romming and J. Songstad, Acta Chem. Scand.,
Ser. A., 1982, 36, 665.
8 NMR parameters for Rh and Pt complexes: [(pyrr)3P]2Rh(CO)Cl: d
98.5, 146 Hz; [(pyrr)2PhP]2Rh(CO)Cl: d 88.2, 136 Hz; [(pyrr)2-
MeP]2Rh(CO)Cl: d 95.2, 130 Hz; [(pyrr)2ButP]2Rh(CO)Cl: d 114.6,
133 Hz. Pt complexes: 6: d 40.7, 4950 Hz; 7: d 46.1, 4358 Hz; 8: d 46.4,
4232 Hz; ligand 5 does not give cis-L2PtCl2 on reaction with Pt(cod)Cl2.
A trans-L2PtCl2 complex can most conveniently be prepared from
Zeise’s Salt, K[PtCl3(C2H4)] d 83.5, 2716 Hz.
9 S. Vastag, B. Heil and L. Marko, J. Mol. Catal., 1979, 5, 189.
10 D. de Montauzon and R. Poilblanc, J. Organomet. Chem., 1975, 93,
397.
The X-ray structure of trans-[P(N-pyrr)3]2Rh(CO)Cl 2 shows
two of the pyrrolidine rings in a given P(N-pyrr)3 fragment to
have planar N atoms (sum of angles around N = 354–360°) and
one tetrahedral N atom (sum of angles around N = 347, 350°)
with a 0.02 Å longer P–N bond length [av. 1.667(3) vs. 1.688(3)
Å]. We therefore expected the crystal structure of [P(N-
pyrr)3]2PtCl2 to show this phenomenon. The crystal structure of
[P(N-pyrr)3]2PtCl2 shows the expected cis square planar Pt
complex, but to our surprise, the sum of angles around each N
was similar (356–360°) and planar. The P–N bond lengths
[1.628(10), 1.721(11), 1.642(11), 1.659(10), 1.678(12) and
1.678(9) Å] do not show any particular pattern.
The crystal structure of [MeP(N-pyrr)2]2PtCl2 8 has two
independent molecules in each unit cell, but there are no drastic
differences between the two molecules. Complex 8 shows a
similar coordination environment to complex 6, with fairly
similar Pt–Cl and Pt–P bond lengths. The angle P(1)–Pt(1)–P(2)
between the phosphines is considerably smaller than in complex
6 [93.90(8), 93.37(7) vs. 98.24(10)°], and indicates that MeP(N-
pyrr)2 is less sterically demanding than P(N-pyrr)3. As a result
of this, the angle between the Cl ligands is slightly larger in
complex 8 [87.01(9), 86.14(8) vs. 85.08(11)°]. The bond
lengths and angles about the N atoms are again somewhat
surprising. Each phosphine has one planar N (sum of angles
from the four phosphine ligands in the two independent
molecules: 356.6, 359.5, 359.5, 356.4°), and in each of the four
phosphine molecules present, the other N atom shows a slight
tetragonal distortion (sum of angles: 353.3, 353.5, 354.0,
351.8°), and slightly longer P–N bond length [average bond
lengths: 1.683(6) vs. 1.643(7) Å].
11 S. Franks and F. R. Hartley, Inorg. Chim. Acta, 1981, 47, 235.
12 W. Strohmeier, W. Rehder-Strirnweiss and G. Reischig, J. Organomet.
Chem., 1971, 17, 393.
13 R. L. Harlow, S. A. Westcott, D. L. Thorn and R. T. Baker, Inorg.
Chem., 1992, 31, 323.
14 N. J. Colville, E. A. Darling, A. W. Hearn and P. Johnston, J.
Organomet. Chem., 1987, 328, 375.
15 Crystal data for 6: C24.50H49Cl3N6P2Pt, M = 791.08, orthorhombic, a =
18.3979(9), b = 10.7098(6), c = 17.2722(6) Å, U = 3403.3(3) Å3, T
= 293 K, space group Pna21, Z = 8, m = 4.476 mm21, 14076
reflections measured, 4808 independent reflections (Rint = 0.0983),
Final R1 = 0.0428, Final wR(F2) was 0.0929. For 8: C18H38Cl2N4P2Pt,
M = 638.45, monoclinic, a = 8.5068(3), b = 26.2926(10), c =
21.6988(8) Å, b = 90.27(1)°, U = 4853.2(3) Å3, T = 293 K, space
group P21/n, Z = 8, m = 6.146 mm21, 21101 reflections measured,
6979 independent reflections (Rint = 0.0520), Final R1 = 0.0366, Final
wR(F2) was 0.0774 (all data). CCDC 182/1778. See http://www.rsc.org/
suppdata/cc/b0/b004893n/ for crystallographic files in .cif format.
The crystallographically determined cone angles of P(pyrr)3
and MeP(pyrr)2 are 122 and 110°, respectively. These values
refer to 2/3 of the sum of the largest possible angle observed
between the Pt centre and the centre H atoms on the phosphine
2066
Chem. Commun., 2000, 2065–2066