Orthometalation of Functionalized Phosphinoamines with Late Transition Metal Complexes

Article abstract of DOI:10.1021/om990363b

The neutral metal complexes CiS-[Pt(CH₃)₂-{o-Ph₂PN(H)C₆H ₄C(O)CH₃-P}₂] and [RhCl₂(Cp*){o-Ph₂-PN(H)C₆H ₄C(O)Ph-P}] are excellent precur

Full text of DOI:10.1021/om990363b

Organometallics 1999, 18, 3255-3257
3255
Or th om eta la tion of F u n ction a lized P h osp h in oa m in es
w ith La te Tr a n sition Meta l Com p lexes
Kirsty G. Gaw, Alexandra M. Z. Slawin, and Martin B. Smith*
Department of Chemistry, Loughborough University,
Loughborough, Leicestershire, LE11 3TU, U.K.
Received May 14, 1999
Summary: The neutral metal complexes cis-[Pt(CH3)2-
{o-Ph2PN(H)C6H4C(O)CH3-P}2] and [RhCl2(Cp*){o-Ph2-
prising given the recent interest displayed in this unique
class of ligand.10 Here we describe the synthesis of two
new functionalized phosphinoamine ligands and report
our preliminary orthometalation studies of these coor-
dinated ligands at platinum(II) and rhodium(III) metal
centers.
PN(H)C6H4C(O)Ph-P}] are excellent precursors for new
2
five-membered M-P-N-C-C metallacycles via σ(Csp
-
H) bond activation. The synthesis and characterization
including the molecular structures of cis-[Pt{o-Ph2PN-
(H)C6H3C(O)CH3-P,C}2]‚OEt2 and [RhCl(Cp*){o-Ph2PN-
(H)C6H3C(O)Ph-P,C}]‚0.5CHCl3 are reported.
The new ligands o-Ph2PN(H)C6H4X [X ) C(O)CH3, 1;
X ) C(O)Ph, 2], closely related to Ph2PN(H)C6H5,11 were
successfully synthesized from cheap, commercially avail-
able Ph2PCl and o-H2NC6H4X in respectable yields (ca.
70%). Moreover this general procedure has allowed us
Orthometalation reactions constitute an important
class of reaction that have been widely employed in the
synthesis of numerous organometallic compounds.1
Whereas the predominance of these cyclometalated
compounds are mononuclear, several recent examples
of bi- and tetranuclear complexes have been described.2
In large, such interest derives from the use of these
compounds in disparate areas including catalysis,3
organic synthesis,4 in material science,5 and resolution
procedures6 and as antitumor agents.7
The chemical literature contains a plethora of reports
describing orthometalated triarylphosphine or phos-
phite complexes.1a,3,6,8 Furthermore the first example of
a cyclometalated compound with a water-soluble tri-
arylphosphine, TPPTS [tris(3-sodium sulfonatophenyl)-
phosphine], was recently described by Pruchnik and co-
workers.9 Although cleavage of aromatic C-H bonds in
tertiary phosphines and phosphites is well-known, to
the best of our knowledge, examples with phosphinoam-
ines bearing one (or more) combinations of P-N/P-C
bonds have not been investigated. This is rather sur-
to routinely prepare these ligands in batches up to ca.
10 g. Both 1 and 2 were characterized by the usual
spectroscopic and analytical techniques.12 The 31P{1H}
NMR spectra (36.2 MHz) of 1 (and 2) show single P
resonances at δ(P) 25.6 (for 1) and 26.5 ppm (for 2),
which is typical for this class of ligand.10c Furthermore
we formulate 1 and 2 as monosubstituted compounds
since in the H NMR spectra a small J (PH) coupling
of ca. 7.5 Hz was observed. Oxidation of 1 with 30%
aqueous hydrogen peroxide gave the phosphorus(V)
compound o-Ph2P(O)N(H)C6H4C(O)CH3, 3, whose mo-
lecular structure has been determined (Figure 1). The
X-ray crystal structure13 is broadly as anticipated, with
a P(1)-O(1) bond length of 1.472(2) (molecule 1) and
1.470(2) Å (molecule 2), shorter than that observed in
Ph2PN(H)P(O)Ph2 [1.508(2) Å], which exists in the solid
state as a hydrogen-bonded dimer pair.10c Furthermore
there is also a strong intramolecular N-H‚‚‚O hydrogen
bond [N(1)‚‚‚O(19) 2.62 Å, H(1)‚‚‚O(19) 1.78 Å; N(1)-
H(1)‚‚‚O(19) 143° (molecule 1); N(21)‚‚‚O(21) 2.64 Å,
H(21)‚‚‚O(21) 1.82 Å; N(21)-H(21)‚‚‚O(21) 141° (mol-
ecule 2)].
1
2
* To whom correspondence should be addressed. Fax number: +44
(01509) 223925. E-mail: m.b.smith@lboro.ac.uk.
(1) For recent examples, see: Cromhout, N. L.; Gallagher, J . F.;
Manning, A. R.; Paul, A. Organometallics 1999, 18, 1119-1121. (b)
Gu¨l, N, Nelson, J . H. Organometallics 1999, 18, 709-725.
(2) (a) Bosque, R.; Lo´pez, C.; Solans, X.; Font-Bardia, M. Organo-
metallics 1999, 18, 1267-1274. (b) O’Keefe, B. J .; Steel, P. J . Orga-
nometallics 1998, 17, 3621-3623.
(3) (a) Albisson, D. A.; Bedford, R. B.; Lawrence, S. E.; Scully, P. N.
Chem. Commun. 1998, 2095-2096. (b) Shaw, B. L.; Perera, S. D.;
Staley, E. A. Chem. Commun. 1998, 1361-1362. (c) Luo, F.-T.;
J eevanandam, A.; Basu, M. K. Tetrahedron Lett. 1998, 39, 7939-7942.
(d) Herrmann, W. A.; Brossmer, C.; Reisinger, C.-P.; Riermeier, T. H.;
O¨ fele, K.; Beller, M. Chem. Eur. J . 1997, 3, 1357-1364. (e) Herrmann,
W. A.; Brossmer, C.; O¨ fele, K.; Reisinger, C.-P.; Priermeier, T.; Beller,
M., Fischer, H. Angew. Chem., Int. Ed. Engl. 1995, 34, 1844-1848. (f)
Beller, M.; Fischer, H.; Herrmann, W. A.; O¨ fele, K.; Brossmer, C.
Angew. Chem., Int. Ed. Engl. 1995, 34, 1848-1849.
Ligand displacement of cod (cod ) cycloocta-1,5-diene)
from [Pt(CH3)2(cod)] with 2 equiv of 1 in dichlo-
romethane gave cis-[Pt(CH3)2(1)2], 4 (Scheme 1). The
31P{1H} NMR spectrum of 4 showed a single resonance
(4) Ryabov, A. D. Synthesis 1985, 233-252.
(5) Bruce, D. W. J . Chem. Soc., Dalton Trans. 1993, 2983-2989.
(6) Airey, A. L.; Swiegers, G. F.; Willis, A. C.; Wild, S. B. J . Chem.
Soc., Chem. Commun. 1995, 693-694.
(7) Navarro-Ranninger, C.; Lo´pez-Solera, I.; Gonza´lez, V. M.; Pe´rez,
J . M.; Alvarez-Valde´s, A.; Mart´ın, A.; Raithby, P. R.; Masaguer, J . R.;
Alonso, C. Inorg. Chem. 1996, 35, 5181-5187.
(10) (a) Zhang, F.-Y.; Pai, C.-C.; Chan, A. S. C. J . Am. Chem. Soc.
1998, 120, 5808-5809. (b) Shen, J .; Stevens, E. D.; Nolan, S. P.
Organometallics 1998, 17, 3875-3882. (c) Bhattacharyya, P.; Slawin,
A. M. Z.; Smith, M. B.; Woollins, J . D. Inorg. Chem. 1996, 35, 3675-
3682.
(11) Hudson, R. F.; Searle, R. J . G.; Devitt, F. H. J . Chem. Soc. C
1966, 1001-1004.
(8) Bedford, R. B.; Chaloner, P. A.; Hitchcock, P. B. J . Chem. Soc.,
Chem. Commun. 1995, 2049-2050.
(9) Pruchnik, F. P.; Starosta, R.; Smolenski, P.; Shestakova, E.;
Lahuerta, P. Organometallics 1998, 17, 3684-3689.
10.1021/om990363b CCC: $18.00 © 1999 American Chemical Society
Publication on Web 07/30/1999

3256 Organometallics, Vol. 18, No. 17, 1999
Communications
Sch em e 1
F igu r e 1. Molecular structure of 3, shown with 50%
thermal ellipsoids. Only one of the two independent
molecules is depicted. All C-H hydrogen atoms are omitted
for clarity. Selected bond distances (Å) and angles (deg)
(equivalent values for the second molecule are given in
square brackets): P(1)-O(1) 1.472(2) [1.470(2)], P(1)-N(1)
1.654(2) [1.660(2)], C(19)-O(19) 1.226(3) [1.228(2)]; O(1)-
P(1)-N(1) 115.84(8) [117.04(9)].
Sch em e 2
at δ(P) 51.3 ppm flanked by 195Pt satellites [1J (PtP) 2028
Hz]. Bridge cleavage of the dimer [{RhCl2(Cp*)}2] with
2 equiv of 2 in dichloromethane gave the mononuclear
compound [RhCl2(Cp*)2], 5, in good yield. The 31P{1H}
(12) Selected spectroscopic data for compounds 1-7. For 1: NMR
(CDCl3) 31P{1H}: δ 25.6. 1H δ 9.71 (NH) [2J (PH) 7.5 Hz], 7.76-6.68
(aromatic H), 2.57 (CH3). IR (KBr): ν(NH) 3212, 3198, 3190 and
ν(CO) 1633 cm-1. FAB MS: m/z 319 (M+). (Found: C, 74.57; H, 5.91;
N, 4.32. C20H18NOP‚0.25H2O requires C, 74.17; H, 5.76; N, 4.32). For
2: NMR (CDCl3) 31P{1H}: δ 26.5. 1H δ 9.23 (NH) [2J (PH) 7.8 Hz], 7.66-
6.67 (aromatic H). IR (KBr): ν(NH) 3314, 3237 and ν(CO) 1619, 1612
cm-1. FAB MS: m/z 381 (M+). (Found: C, 77.26; H, 5.24; N, 3.21.
C25H20NOP‚0.25H2O requires C, 77.80; H, 5.31; N, 3.63). For 3: NMR
(CDCl3) 31P{1H}: δ 18.5. 1H δ 10.70 (NH) [2J (PH) 8.3 Hz], 7.94-6.90
(aromatic H), 2.66 (CH3). IR (KBr): ν(NH) 3097, 3072, ν(CO) 1640 and
ν(PO) 1208 cm-1. (Found: C, 71.44; H, 5.39; N, 4.07. C20H18NO2P
requires C, 71.63; H, 5.42; N, 4.18). For 4: NMR (CDCl3) 31P{1H}: δ
51.3 [1J (PtP) 2028 Hz]. 195Pt{1H}: δ -4502. 1H δ 10.01 (NH) [3J (PtH)
21.5 Hz], 7.95-6.71 (aromatic H), 2.56 (CH3), 0.54 (Pt-CH3), [2J (PtH)
69.2, 3J (PH) 6.5 Hz]. IR (KBr): ν(NH) 3163, 3129 and ν(CO) 1643 cm-1
.
(Found: C, 57.95; H, 4.57; N, 3.21. C42H42N2O2P2Pt requires C, 58.39;
H, 4.91; N, 3.24%). For 5: NMR (CDCl3) 31P{1H}: δ 55.5 [1J (RhP) 154
Hz]. 1H δ 9.75 (NH) [2J (PH) 11.5 Hz], 8.14-7.03 (aromatic H), 1.42
(C5(CH3)5) [4J (PH) 3.8 Hz]. IR (KBr): ν(NH) 3175 and ν(CO) 1628 cm-1
.
(Found: C, 59.48; H, 5.18; N, 1.69. C35H35NOPRhCl2‚0.25CH2Cl2
requires C, 59.48; H, 4.99; N, 1.97). For 6: NMR (CDCl3) 31P{1H}: δ
88.9 [1J (PtP) 2191 Hz], 88.0 [1J (PtP) 3238 Hz]. 195Pt{1H}: δ -4510,
-4636. 1H δ 10.5 [3J (PtH) 57.6 Hz], 10.1 [3J (PtH) 40.3 Hz] (NH), 7.86-
6.28 (aromatic H), 2.53, 2.49 (CH3). IR (KBr) ν(NH) 3191 and ν(CO)
1634 cm-1. FAB MS: m/z 832 (M+) (Found: C, 57.38; H, 4.39; N, 3.21.
NMR spectrum of 5 showed a doublet centered at δ(P)
1
55.5 ppm with a J (RhP) of 154 Hz.12
Thermal activation of a C-H bond is a common
procedure for synthesizing orthometalated complexes.
Accordingly when 4 (or 5) was refluxed in xylene for
between 24-48 h under a nitrogen atmosphere (Scheme
2), the orthometalated compounds [Pt{o-Ph2PN(H)-
C6H3C(O)CH3-P,C}2], 6, and [RhCl(Cp*){o-Ph2PN(H)-
C6H3C(O)Ph-P,C}], 7, were obtained in reasonable yields
(64% for 6, 53% for 7).14 When the thermolysis of 5 was
performed in the presence of excess NEt3, several
phosphorus-containing species, in addition to 7, were
identified. The 31P{1H} NMR spectra of 6 (and 7) were
C
40H34N2O2P2Pt requires C, 57.76; H, 4.13; N, 3.37). For 7: NMR
(CDCl3) 31P{1H}: δ 105.4 [1J (RhP) 172 Hz]. 1H δ 9.75 (NH), 7.75-
6.55 (aromatic H), 1.48 (C5(CH3)5) [4J (PH) 3.4 Hz]. IR (KBr): ν(NH)
3231 and ν(CO) 1608 cm-1. FAB MS: m/z 655 (M+) (Found: C, 61.18;
H, 5.01; N, 1.79. C35H34NOClPRh‚0.5CH2Cl2 requires C, 61.21; H, 5.08;
N, 2.01). All 1H NMR spectra were recorded at 250 MHz and referenced
to external TMS, whereas 31P{1H} NMR spectra were recorded at 36.2
MHz and referenced to external phosphoric acid.
(13) Structural data were collected using a Siemens SMART dif-
fractometer using graphite-monochromated Mo KR radiation. Crystal
data for 3:
C20H18NO2P, 335.32, monoclinic, space group P21/c, a )
12.343(1) Å, b ) 11.2683(1) Å, c ) 25.1886(2) Å, â ) 103.54(1)°, V )
3406.07(4) Å3, Z ) 8, Dc ) 1.308 g/cm3, µ ) 0.173 mm-1, R (Rw) 0.045
(0.096) for 4873 observed reflections. 6: C40H34N2OP2Pt‚OEt2 905.84,
monoclinic, space group C2/c, a ) 25.1102(4) Å, b ) 10.2756(1) Å, c )
15.8647(2) Å, â ) 99.298(1)°, V ) 4039.66(9) Å3, Z ) 4, Dc ) 1.489
g/cm3, µ ) 3.593 mm-1, R (Rw) 0.045 (0.109) for 4635 observed
(14) A typical procedure is illustrated here for the synthesis of
compound 6. Under a nitrogen atmosphere, a suspension of 4 (80 mg,
0.093 mmol) in xylene (20 mL) was heated to reflux for ca. 48 h. The
solvent was reduced in vacuo, the solid residue extracted with CH2Cl2
(5 mL), and this extract filtered through Celite. The solvent volume
was reduced and diethyl ether (20 mL) added to afford 6, with a further
crop isolated from the filtrate (49 mg, 64%).
reflections. 7:
C35H34ClNOPRh‚0.5CHCl3, 713.65, monoclinic, space
group P21/a, a ) 14.1667(6) Å, b ) 31.3669(14) Å, c ) 15.2768(7) Å, â
) 106.843(1)°, V ) 6497.3(5) Å3, Z ) 8, Dc ) 1.459 g/cm3, µ ) 0.810
mm-1, R (Rw) 0.047 (0.087) for 9291 observed reflections.

Communications
Organometallics, Vol. 18, No. 17, 1999 3257
F igu r e 2. Molecular structure of 6, shown with 50%
thermal ellipsoids. All C-H hydrogen atoms and solvent
are omitted for clarity. Selected bond distances (Å) and
angles (deg): Pt(1)-C(13) 2.090(5), Pt(1)-P(1) 2.2726(12),
P(1)-N(1) 1.692(5), C(19)-O(19) 1.221(8); C(13)-Pt(1)-
C(13*) 95.9(2), C(13)-Pt(1)-P(1*) 170.63(13), C(13)-Pt-
(1)-P(1) 80.59(13), P(1)-Pt(1)-P(1*) 104.20(6), Pt(1)-
P(1)-N(1) 101.9(2).
F igu r e 3. Molecular structure of 7, shown with 50%
thermal ellipsoids. Only one of the two independent
molecules is depicted. All C-H hydrogen atoms and solvent
are omitted for clarity. Selected bond distances (Å) and
angles (deg) (equivalent values for the second molecule are
given in square brackets): Rh(1)-P(1) 2.244(2) [2.240(2)],
Rh(1)-Cl(1) 2.394(2) [2.385(2)], Rh(1)-C(18) 2.063(6), [2.055-
(6)], P(1)-N(1) 1.680(5) [1.684(5)], C(19)-O(19) 1.244(7)
[1.239(7)]; P(1)-Rh(1)-Cl(1) 92.76(7) [91.46(6)], P(1)-Rh-
(1)-C(18) 81.2(2) [80.9(2)], Cl(1)-Rh(1)-C(18) 82.9(2) [84.3-
(2)], Rh(1)-P(1)-N(1) 104.9(2) [104.6(2)].
particularly informative, with large (ca. 40-50 ppm)
downfield shifts in δ(P) consistent with the coordinated
PIII center being part of a five-membered M-P-N-C-C
metallacycle.12 In the case of platinacycle 6 two closely
spaced singlets at δ(P) 88.9 [1J (PtP) 2191 Hz] and 88.0
ppm [1J (PtP) 3238 Hz], in an approximate ratio of ca.
1:1 (CDCl3 solution), are assigned to a mixture of cis
and trans isomers, respectively. This is further corrob-
orated by the observation of two well-separated NH
resonances, centered at ca. 10 ppm and with 195Pt satel-
a η5 Cp*, one chloride, and an η2 [o-Ph2PN(H)C6H3C-
(O)Ph-P,C]- orthometalated ligand. The Rh-P distance
[2.244(2) (molecule 1); 2.240(2) Å (molecule 2)] is broadly
as expected. The carbonyl moieties in compounds 6 and
7 are both involved in strong intramolecular hydrogen
bonding to the N-H proton [for 6, N(1)‚‚‚O(19) 2.60 Å,
H(1)‚‚‚O(19) 1.80 Å; N(1)-H(1)‚‚‚O(19) 138°; for 7,
N(1)‚‚‚O(19) 2.63 Å, H(1)‚‚‚O(19) 1.85 Å; N(1)-
H(1)‚‚‚O(19) 135° (molecule 1) and N(41)‚‚‚O(59) 2.66
Å, H(41)‚‚‚O(59) 1.91 Å; N(41)-H(41)‚‚‚O(59) 131° (mol-
ecule 2)]. The structures of 6 and 7 represent extremely
rare examples of crystallographically characterized
compounds containing a M-P-N-C-C chelate ring.17
The utility of phosphinoamine ligands, R2PN(H)R (R
) aryl substituent), has allowed for the first time new
examples of cyclometalated M-P-N-C-C compounds
to be prepared. This genre of complex could prove
beneficial in a number of applications and is currently
an area under further investigation in our laboratory.
1
lites, in the H NMR spectrum of 6. In the IR spectrum
of 6 the similarity of νCdO with that of 1 supports the
absence of any carbonyl interaction with the platinum
center. Monitoring the thermolysis of 4 by 31P{1H} NMR
revealed the formation of an intermediate species,
tentatively assigned as [Pt(CH3){o-Ph2PN(H)C6H3C(O)-
CH3-P,C}(1)] [δ(P) 52.2, 1J (PtP) 2287 Hz (1 trans to
orthometalated σ bonded C); 86.4 ppm, 1J (PtP) 2067
Hz].15 No attempts to separate the isomers of 6 nor test
for methane formation were pursued.
The X-ray structures of 6 and 7 are depicted in
Figures 2 and 3, respectively.13 Suitable crystals of 6
were grown from slow diffusion of Et2O into a CDCl3/
CH2Cl2 solution (cis:trans ratio of ca. 5:1, established
first by 31P{1H} NMR). In 6 the molecule is disposed
about a crystallographic 2-fold axis on which the plati-
num lies. The platinum(II) center is approximately
square-planar [C(13)-Pt(1)-C(13*) 95.9(2), C(13)-Pt-
(1)-P(1*) 170.63(13), C(13)-Pt(1)-P(1) 80.59(13), P(1)-
Pt(1)-P(1*) 104.20(6)°] with two chelating orthometa-
lated [o-Ph2PN(H)C6H3C(O)CH3-P,C]- ligands arranged
in a cis geometry. Furthermore the unique PtPNC2 five-
membered ring is slightly puckered [Pt(1)-P(1)-N(1)-
C(14)-C(13) mean plane, with maximum deviation of
N(1) 0.18 Å out of this plane]. The Pt(1)-C(13) distance
[2.090(5) Å] is longer than that in [Pt(dppe)Ph2] [dppe
) 1,2-(diphenylphosphino)ethane] [2.05(1) Å]16 presum-
ably as a consequence of the different π-acceptor proper-
ties of the two phosphorus-containing ligands. The
structure of 7 reveals a classic three-legged piano stool
geometry with the rhodium(III) center coordinated by
Ack n ow led gm en t. We should like to thank the
EPSRC for a studentship (K.G.G.), Infineum UK Ltd
for financial support, and J ohnson Matthey plc for loans
of precious metals. Fast atom bombardment (FAB) mass
spectra were run by the EPSRC mass spectrometry
service at Swansea.
Su p p or tin g In for m a tion Ava ila ble: Tables of complete
crystallographic data for 3, 6, and 7. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM990363B
(15) Gaw, K. G.; Slawin, A. M. Z.; Smith, M. B. Unpublished results.
(16) Braterman, P. S.; Cross, R. J .; Manojlovic-Muir, L.; Muir, K.
W.; Young, G. B. J . Organomet. Chem. 1975, 84, C40-C42.
(17) Scherer, O. J .; Flo¨rchinger, M.; Go¨bel, K.; Kaub, J .; Sheldrick,
W. S. Chem. Ber. 1988, 121, 1265-1270.