A lanthanide phosphinidene complex: Synthesis, structure, and phospha-wittig reactivity

Article abstract of DOI:10.1021/ja7105306

The first lanthanide complex featuring a phosphinidene functional group has been prepared and isolated. Preliminary reactivity studies demonstrate that the lutetium(III) phosphinidene complex, [{2-(ⁱPr₂P)-4-Me-C₆H₃}₂NLu]₂(μ-PMes)₂, behaves as a phospha-Wittig reagent with aldehydes and ketones to give the corresponding phosphaalkenes. Attempts to use the bulky phosphine H₂P-2,4,6-^tBu₃-C₆H₂ to kinetically stabilize a terminal phosphinidene resulted in C-H activation of an ortho-^tBu group and formation of a phosphaindole. Copyright

Full text of DOI:10.1021/ja7105306

Published on Web 01/31/2008
A Lanthanide Phosphinidene Complex: Synthesis, Structure, and
Phospha-Wittig Reactivity
Jason D. Masuda,† Kimberly C. Jantunen,† Oleg V. Ozerov,‡ Kevin J. T. Noonan,§ Derek P. Gates,§
Brian L. Scott,† and Jaqueline L. Kiplinger*,†
Los Alamos National Laboratory, Mail Stop J514, Los Alamos, New Mexico 87545, Department of Chemistry,
Brandeis UniVersity, MS015, 415 South Street, Waltham, Massachusetts 02454, and Department of Chemistry,
UniVersity of British Columbia, 2036 Main Mall, VancouVer, British Columbia, V6T 1Z1 Canada
Received November 21, 2007; E-mail: kiplinger@lanl.gov
Although phosphinidene (M ) P) complexes are quite common
in transition metal chemistry, analogous lanthanide derivatives
remain unknown.1 The absence of bridging or terminal lanthanide
phosphinidene complexes is striking since the related actinide series
has two known structurally characterized examples belonging to
uranium: (C5Me5)2U(dPMes*)(OdPMe3) (Mes* ) 2,4,6-tBu3-
C6H2),2 featuring a terminal phosphinidene group, and [(C5Me5)2U-
(OCH3)2]2PH,3 possessing a bridging phosphinidene. Recently,
highly reactive transition metal species such as group 4 alkylidenes,
alkylidynes, phosphinidenes, and imides have been stabilized using
the robust pincer PNP ligand set.4 Herein we report the use of the
PNP ligand 1 to prepare, isolate, and study the first example of a
lanthanide phosphinidene complex.
Figure 1. Molecular structure of complex 3 with thermal ellipsoids
Reaction of the PNP ligands 1 and 2 with Lu(CH2SiMe3)3(THF)2
projected at the 50% probability level. Selected bond distances (Å) and
at room temperature in pentane and toluene, respectively, gave
angles (°): Lu(1)-N(1) 2.244(5), Lu(1)-C(5) 2.307(6), Lu(1)-C(1) 2.322-
the corresponding lutetium bis(alkyl) complexes 3 and 4, respec-
tively, as yellow solids in good isolated yield (Scheme 1).
Whereas 3 is highly soluble in ethers and hydrocarbons and is best
purified by recrystallization from hot TMS2O to give large yellow
(6), Lu(1)-P(1) 2.8534(15), Lu(1)-P(2) 2.8547(15), Lu(1)-C(1)-Si(1)
126.2(3), Lu(1)-C(5)-Si(2) 127.6(3).
Scheme 1
blocks, complex 4 must be triturated from pentane to yield an
1
insoluble yellow powder. The most diagnostic feature in the H
NMR spectra for the two Lu(III) bis(alkyl) complexes are the
methylene resonances at δ -0.33 (3) and δ -0.08 ppm (4). Both
3 and 4 also display signals in their 31P{1H} NMR spectra at δ
14.5 and -4.8 ppm, respectively, downfield from the reson-
ances observed for the free ligands (1, δ -12.9 ppm; 2, δ -18.7
ppm).5 Additionally, the 31P NMR resonance of 3 compares
favorably to the structurally related d0 complex (PNPiPr)ZrMe3 (δ
13.0 ppm).4a
The molecular structure of compound 3 is presented in Figure 1
and reveals a distorted square pyramidal geometry about the Lu-
(III) metal center with one alkyl group in the apical position and
the PNPiPr ligand and the other alkyl group forming the pyramid
base. The Lu-C bond lengths (2.307(6), 2.322(6) Å) fall within
the range typically observed for Lu-CH2SiMe3 bonds.6 The Lu-N
(2.244(5) Å) and Lu-P bonds (2.8534(15), 2.8547(15) Å) are
somewhat shorter than those reported for the structurally related
[{2-(Ph2P)C6H4}2N]Lu(CH2SiMe3)2(THF) (Lu-N ) 2.342(3) Å;
Lu-P ) 2.9096(9), 2.9765(9) Å).7 This difference may be attributed
to the lack of coordinated THF in 3.
As shown in Scheme 1, reaction of a toluene solution of 3 with
1 equiv of MesPH2 (Mes ) 2,4,6-Me3-C6H2) at 80 °C for 12 h
afforded the Lu(III) phosphinidene complex 5 as a cherry red solid
in 52% isolated yield. The 31P{1H} NMR spectrum of 5 exhibits a
diagnostic quintet at δ 186.8 ppm coupled to a triplet at δ 18.1
ppm (2JP-P ) 14.6 Hz) consistent with two bridging phosphinidene
units between two (PNPiPr)Lu fragments.
The most interesting aspect of the structure is the asymmetric
Lu2P2 core. The Lu-Lu distance of 3.9353(5) Å is longer than the
sum of their ionic radii (1.722 Å).8 The two shorter bonds of the
core, Lu(1)-P(3) (2.6031(16) Å) and Lu(2)-P(4) (2.5973(15) Å),
are on average ∼0.06 Å shorter than Lu(1)-P(4) (2.6724(14) Å)
and Lu(2)-P(3) (2.6527(16) Å) as well as shorter than the Lu-P
bond distances reported for the few known lutetium phosphide
complexes (e.g., [Me2Si(C5Me4)(µ-PPh)Lu(CH2SiMe3)]2, Lu-P )
2.826(1), 2.786(1) Å; [Me2Si(C5Me4)(µ-PCy)Lu(CH2SiMe3)]2, Lu-P
† Los Alamos National Laboratory.
‡ Brandeis University.
§ University of British Columbia.
9
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J. AM. CHEM. SOC. 2008, 130, 2408-2409
10.1021/ja7105306 CCC: $40.75 © 2008 American Chemical Society

C O M M U N I C A T I O N S
In summary, the first lanthanide complex featuring a phosphin-
idene functional group has been prepared and isolated. Although
the large ionic radii of the lanthanide ions make it challenging to
introduce enough steric saturation to stabilize a terminal phosphin-
idene, these results demonstrate that the formation of lanthanide
phosphinidenes is possible and that the phosphinidene dimer 5
behaves as a nucleophilic phosphinidene transfer reagent. Efforts
focused on stabilizing a terminal lanthanide-based phosphinidene
complex by modifying both the supporting ligand and the substitu-
ent on the phosphorus atom are currently underway in our
laboratory.
Acknowledgment. For financial support, we acknowledge
LANL (Director’s PD Fellowship to J.D.M.), the LANL G. T.
Seaborg Institute (PD fellowship to J.D.M.; summer student
fellowship to K.C.J.), the Division of Chemical Sciences, Office
of Basic Energy Sciences, the LANL LDRD Program (J.L.K.), the
NSERC of Canada for Discovery & Tools grants (D.G.) and a PGS
D scholarship (K.J.T.N.), the NSF (CHE-0517798), and the Sloan
& Dreyfus Foundations (O.V.O.). We are thankful to Y. Zhu, M.
Puri, and Dr. S. Gatard for the synthesis of initial samples of 1 and
2 used in this work.
Figure 2. Molecular structure of complex 5 with thermal ellipsoids
projected at the 50% probability level. Selected bond distances (Å) and
angles (°): Lu(1)-P(3) 2.6031(16), Lu(1)-P(4) 2.6724(14), Lu(2)-P(3)
2.6527(16), Lu(2)-P(2) 2.5973(15), Lu(1)-N(1) 2.296(4), Lu(2)-N(2)
2.295(4), Lu(1)-P(3)-Lu(2) 96.96(5), Lu(1)-P(4)-Lu(2) 96.61(5), P(3)-
Lu(1)-P(4) 82.90(5), P(4)-Lu(2)-P(3) 83.40(5).
) 2.817(1), 2.789(1) Å; [Me2Si(C5Me4)(PPh)Lu(µ-H)]2(THF)3,
Lu-P ) 2.788(2), 2.861(2) Å; [Me2Si(C5Me4)(PMes*)Lu(µ-H)-
(THF)]2, Lu-P ) 2.683(1) Å; [Cp2Lu{µ-PPh2}2Li(tmeda)], Lu-P
) 2.782(1), 2.813(2) Å).6a,9
Supporting Information Available: Full experimental and char-
acterization details for all new compounds. Crystallographic data for 3
and 5. This material is available free of charge via the Internet at http://
pubs.acs.org.
Interestingly, the mesityl rings are nearly planar with the Lu2P2
core, with Lu(1)-P(4)-C(10)-C(11) and Lu(2)-P(3)-C(1)-C(2)
dihedral angles of 7.11 and 5.81°, respectively. This likely
minimizes unfavorable interactions between the ortho-CH3 groups
on the mesityl rings and the iPr groups on the PNP ligand. Finally,
the sum of the angles around P(3) and P(4) are 358.9 and 356.5°,
respectively, allowing for π-donation of the phosphorus lone pairs
to the Lu atoms. All of these combined structural features are
consistent with the formulation of complex 5 as an asymmetric
dimer of the terminal phosphinidene, (PNPiPr)LudPMes, with a
bond order greater than 1 in the Lu(1)-P(3) and Lu(2)-P(4)
interactions.
References
(1) (a) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds; Wiley-
Interscience: New York, 1988. (b) Cowley, A. H. Acc. Chem. Res. 1997,
30, 445-451. (c) Lammertsma, K. Top. Curr. Chem. 2003, 229, 95-
119. (d) Giesbrecht, G. R.; Gordon, J. C. Dalton Trans. 2004, 2387-
2393. (e) Clark, D. L.; Gordon, J. C.; Hay, P. J.; Poli, R. Organometallics
2005, 24, 5447-5787. (f) Weber, L. Eur. J. Inorg. Chem. 2007, 4095-
4117.
(2) Arney, D. S. J.; Schnabel, R. C.; Scott, B. L.; Burns, C. J. J. Am. Chem.
Soc. 1996, 118, 6780-6781.
(3) Duttera, M. R.; Day, V. W.; Marks, T. J. J. Am. Chem. Soc. 1984, 106,
2907-2912.
(4) (a) Weng, W.; Yang, L.; Foxman, B. M.; Ozerov, O. V. Organometallics
2004, 23, 4700-4705. (b) Mindiola, D. J. Acc. Chem. Res. 2006, 39, 813-
821. (c) Zhao, G.; Basuli, F.; Kilgore, U. J.; Fan, H.; Aneetha, H.;
Huffman, J. C.; Wu, G.; Mindiola, D. J. J. Am. Chem. Soc. 2006, 128,
13575-13585. (d) Bailey, B. C.; Fan, H.; Huffman, J. C.; Baik, M. H.;
Mindiola, D. J. J. Am. Chem. Soc. 2007, 129, 8781-8793. (e) Liang, L.
C. Coord. Chem. ReV. 2006, 250, 1152-1177.
Preliminary reactivity studies demonstrate that 5 behaves simi-
larly to known nucleophilic phosphinidene systems such as [(N3N)-
t
TadPR] (R ) Ph, Cy, Bu; N3N ) (Me3SiNCH2CH2)3N)10 and
Cp2Zr(dPMes*)(PMe3) (Figure 2).11 Complex 5 reacts smoothly
as a phospha-Wittig reagent with aldehydes and ketones to give
the corresponding phosphaalkenes. For example, reaction of 5 with
pivalaldehyde affords (E)-MesPdC(H)tBu (48% yield, 31P NMR
δ 227.1 ppm)12 and with benzophenone yields MesPdCPh2 (72%
yield, 31P NMR δ 234.0 ppm).13 Concomitant formation of
[(PNPiPr)LuO]x is likely, but to date, we have not been able to
ascertain the fate of the lutetium byproduct.
Attempts to disrupt the dimer and stabilize a terminal phosphin-
idene using Lewis bases were unsuccessful (PMe3, tmeda, DMAP,
or bipyridines) or resulted in decomposition (OdPMe3). Kinetic
stabilization was also explored using the sterically demanding
phosphine, Mes*PH2. Reaction of a toluene-d8 solution of 3 or 4
with Mes*PH2 at 80 °C for 7-12 h resulted in quantitative
formation of the phosphaindole 6 as determined by 31P NMR
spectroscopy (eq 1).
(5) (a) Fan, L.; Foxman, B. M.; Ozerov, O. V. Organometallics 2004, 23,
326-328. (b) Fan, L. Ph.D. Thesis, Brandeis University, 2006.
(6) For examples, see: (a) Tardif, O.; Nishiura, M.; Hou, Z. Tetrahedron
2003, 59, 10525-10539. (b) Cameron, T. M.; Gordon, J. C.; Scott, B. L.
Organometallics 2004, 23, 2995-3002. (c) Jantunen, K. C.; Scott, B. L.;
Hay, P. J.; Gordon, J. C.; Kiplinger, J. L. J. Am. Chem. Soc. 2006, 128,
6322-6323.
(7) Zhang, L.; Suzuki, T.; Luo, Y.; Nishiura, M.; Hou, Z. Angew. Chem., Int.
Ed. 2007, 46, 1909-1913.
(8) Shannon, R. D. Acta Cryst. 1976, A32, 751-767.
(9) Schumann, H.; Palamidis, E.; Schmid, G.; Boese, R. Angew. Chem., Int.
Ed. Engl. 1986, 25, 718-719.
(10) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Angew. Chem., Int. Ed.
Engl. 1993, 32, 756-759.
(11) (a) Stephan, D. W. Angew. Chem., Int. Ed. 2000, 39, 314-329 and
references therein. (b) Breen, T. L.; Stephan, D. W. J. Am. Chem. Soc.
1995, 117, 11914-11921.
(12) Literature (C6D6) δ 228.4 ppm: Brym, M.; Jones, C.; Waugh, M.; Hey-
Hawkins, E.; Majoumo, F. New J. Chem. 2003, 27, 1614-1621.
(13) Literature (CDCl3) δ 233.06 ppm: Klebach, Th. C.; Lourens, R.;
Bickelhaupt, F. J. Am. Chem. Soc. 1978, 100, 4886-4888.
(14) For representative examples, see: (a) Champion, D. H.; Cowley, A. H.
Polyhedron 1985, 4, 1791-1792. (b) Amor, I.; Garcia, M. E.; Ruiz, M.
A.; Saez, D.; Hamidov, H.; Jeffery, J. C. Organometallics 2006, 25, 4897-
4869.
(15) Phosphaindole 6 has been made from Mes*PH2 using transition metal
catalysts. Zr: (a) Masuda, J. D.; Hoskin, A. J.; Graham, T. W.; Beddie,
C.; Fermin, M. C.; Etkin, N.; Stephan, D. W. Chem. Eur. J. 2006, 12,
8696-8707. Rh: (b) Bo¨hm, V. P. W.; Brookhart, M. Angew. Chem., Int.
Ed. 2001, 40, 4694-4696. (c) Stradiotto, M. Fujdala, K. L.; Tilley, T. D.
HelV. Chim. Acta 2001, 84, 2958-2970.
For transition metals, the production of 6 signals the generation of
a transient phosphinidene complex,1c,f which reacts with a C-H
bond on the Mes* ortho-tBu group to give the phosphaindole.14,15
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