P-H and P-P bond activation by Ni(I) and Fe(I) β-diketiminato- complexes

Article abstract of DOI:10.1039/b513892b

Reactions of ((NacNac)Ni)₂(-η³-η³- C₆H₅Me) (NacNac = HC(CMeNC₆H ₃(i-Pr)₂)₂) with PH₂Ph or PHPh ₂ proceeds in a facile manner to afford the Ni(i)-phosphine adducts (NacNac)Ni(PH₂Ph) 1 and (NacNac)Ni(PHPh₂) 2, respectively. The related reactions of the Fe(i) complex (NacNac)Fe(η²-CH ₂CPh₂) 3 with PH₂Ph resulted in the formation of [(NacNac)Fe(²-PPh)]₂ 4. Alternatively 4 was also obtained from the reaction of [(NacNac)Fe(-Cl)]₂ with PHPh ₂ and Na/K. The Ni(ii) di-phosphosphine bridged compound [((NacNac)Ni)₂(⁴-(PPh)₂)] 5 was prepared via reaction of ((NacNac)Ni)₂(-η³-η³-C ₆H₅Me) with P₅Ph₅. Crystallographic data are reported for compounds 1-5. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b513892b

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www.rsc.org/dalton | Dalton Transactions
P–H and P–P bond activation by Ni(I) and Fe(I) b-diketiminato-complexes
Guangcai Bai, Pingrong Wei, Anjan K. Das and Douglas W. Stephan*
Received 30th September 2005, Accepted 25th November 2005
First published as an Advance Article on the web 14th December 2005
DOI: 10.1039/b513892b
3
3
Reactions of ((NacNac)Ni)2(l-g -g -C6H5Me) (NacNac = HC(CMeNC6H3(i-Pr)2)2) with PH2Ph or
PHPh2 proceeds in a facile manner to afford the Ni(I)–phosphine adducts (NacNac)Ni(PH2Ph) 1
2
and (NacNac)Ni(PHPh2) 2, respectively. The related reactions of the Fe(I) complex (NacNac)Fe(g -
CH2CPh2) 3 with PH2Ph resulted in the formation of [(NacNac)Fe(l2-PPh)]2 4. Alternatively 4
was also obtained from the reaction of [(NacNac)Fe(l-Cl)]2 with PHPh2 and Na/K. The Ni(II)
di-phosphosphine bridged compound [((NacNac)Ni)2(l4-(PPh)2)] 5 was prepared via reaction of
3
3
((NacNac)Ni)2(l-g -g -C6H5Me) with P5Ph5. Crystallographic data are reported for compounds 1–5.
Introduction
Experimental
The notion that the chemistry of phosphorus mimics that of
carbon is one that has been asserted for some time. Indeed, the
similarities between these chemistries have spawned the recent text
“Phosphorus: The Carbon Copy”.1 It is this parallel in chemistry
that has also prompted our continuing interest in the activation
of P–H bonds as such studies may offer insight in the longer term
challenge of C–H bond activation. Our earlier explorations of P–
H bond reactivity, focused on the reactivity with early transition
metal complexes. For example, we explored the chemistry of the
zirconocene–phosphinidene derivative Cp2Zr(PR*)(PMe3) in a va-
riety of stoichiometric addition, metathesis and trans-metallation
reactions.2–11 Subsequently, we and others showed that early metal
complexes can catalyze the conversion of primary phosphines
to various polyphosphine oligomers.12–14 This work and related
literature has been recently reviewed.14 Several studies involving
late transition metal complexes in P–H bond activation have also
been reported. Glueck and coworkers have described a variety of
stoichiometricreactions involving P–Hactivation bygroup 8metal
complexes.15–19 Rh-based catalytic conversion of H2P(C6H2t-Bu3)
to phosphacycle HP(C6H2t-Bu2(CMe2CH2)) has been reported
by Tilley and Stradiotto,20 while Bohm and Brookhart reported
the dehydrocoupling of primary and secondary phosphines using
Cp*Rh(CH2CHSiMe3)2.21 In our own efforts to develop the
chemistry of late transition metal species in P–H bond activation
we have initiated a program of study of low valent b-diketiminato-
complexes. In this paper we probe the reactivity of b-diketiminato-
Ni(I) and Fe(I) complexes with primary and secondary phos-
phines. These studies reveal that while Ni(I) simply forms
phosphine adducts, Fe(I) activates P–H bonds to give a phos-
phinidene dimer. Moreover a related diphosphine Ni(II)-dimer
is formed via Ni(I) activation of the P–P bonds of a phosphine
oligomer.
General data
All preparations were performed under an atmosphere of dry, O2-
free N2 employing both Schlenk line techniques and an MBraun
or Vacuum Atmospheres inert atmosphere glove box. Solvents
were purified employing a Grubbs type solvent purification system
manufactured by Innovative Technologies. All organic reagents
were purified by conventional methods. 1H, 31P{ H}, and 13C{ H}
NMR spectra were recorded on Bruker Avance-300 and 500
spectrometers. All spectra were recorded in C6D6 at 25 ◦C unless
otherwise noted. Trace amounts of protonated solvents were used
1
1
1
as a reference for H NMR spectra, while the solvent was used
as a reference for 13C{ H} spectra and chemical shifts for 1H and
1
1
1
13C{ H} spectra are reported relative to SiMe4. 31P{ H} NMR
spectra were referenced to external 85% H3PO4. EPR spectra
were recorded on an X-band Bruker ESP 300E spectrometer. IR
spectra were recorded on a Bruker FTIR spectrometer. Cyclic
voltammetric experiments were performed in CH2Cl2 using a BAS
potentiostat, a Pt electrode with a Ag/AgCl reference electrode,
[NBu4][PF6] (0.1 M) as the supporting electrolyte and a scan
rate of 100 mV s−1. Potentials are referenced to the standard
calomel electrode (SCE). Combustion analyses were done in-house
3
3
employing a Perkin Elmer CHN Analyzer. ((NacNac)Ni)2(l-g -g -
C6H5Me)22 and ((NacNac)Fe(l-Cl)2)Li(THF)2 were prepared by
previously described methods.23 Throughout this paper NacNac
refers to HC(CMeNC6H3(i-Pr)2)2.
Synthesis of (NacNac)Ni(L) L = PH2Ph 1, PHPh2 2. These
compounds were prepared in a similar fashion and thus only one
preparation is detailed. PhPH2 (0.044 g, 0.40 mmol) was added
3
3
to the solution of ((NacNac)Ni)2(l-g -g -C6H5Me) (0.208 g,
0.20 mmol) in toluene (10 mL) at 25 ◦C, the solution became
pale yellow immediately. The mixture was stirred overnight. After
removal of toluene in vacuo and recrystallization in hexane at
−35 ◦C, yellow crystals of 1 (0.19 g) were isolated. 1: Yield:
83%. EPR (toluene, 25 ◦C): g = 2.195, EPR (toluene, −78 ◦C):
g = 2.374, 2.271, 2.133; IR (Nujol, cm−1): 1955 (w), 1916 (w),
1859 (w), 1797 (w), 1697 (w), 1625 (s), 1548 (s), 1525 (s), 1481
Department of Chemistry & Biochemistry, University of Windsor, Windsor,
Ontario, Canada N9B 3P4. E-mail: stephan@uwindsor.ca; Fax: +1 519-
973-7098
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(m), 1459 (s), 1434 (s), 1403 (s), 1382 (m), 1359 (m), 1321 (s),
1265 (m), 1254 (m), 1228 (m), 1177 (s), 1157 (m), 1100 (m),
1085 (m), 1056 (m), 999 (m), 934 (m), 838 (s), 796 (s), 759
(s), 727 (s), 691 (m), 634 (m), 442 (m), 413 (m) cm−1; Anal.
calcd. for C35H48N2NiP (586.5): C 71.7, H 8.3, N 4.8; found:
C 71.5, H 8.7, N 4.6. 2 yellow crystals, yield 0.20 g (75%).
EPR (toluene, 25 ◦C): g = 2.196, EPR (toluene, −78 ◦C):
g = 2.373, 2.272, 2.135; IR (Nujol, cm−1): 1914 (w), 1843 (w), 1795
(w), 1735 (m), 1695 (m), 1649 (m), 1628 (m), 1528 (s), 1456 (s),
1404 (s), 1318 (s), 1259 (s), 1174 (s), 1094 (s), 1053 (s), 1024 (s), 934
(m), 839 (s), 796 (s), 728 (s), 693 (m); Anal. calcd. for C41H52N2NiP
(662.6): C 74.3, H 7.9, N 4.2; found: C 74.5, H 8.1, N 4.2.
was continued for one week at this temperature. After filtration
and subsequent concentration (to 5 mL) in vacuo, the resulting
◦
deep brown solution was kept at −35 C for a week to isolate 4
(0.72 g). After concentration of the filtrate to 3 mL, the solution
was kept at −35 ◦C for three days and an additional crop of 4
(0.21 g) was formed. Yield 0.74 g (67%). IR (Nujol, cm−1): 1926
(w), 1861 (w), 1728 (m), 1696 (w), 1579 (m), 1522 (s), 1461 (s),
1435 (s), 1386 (s), 1337 (s), 1315 (s), 1259 (s), 1176 (s), 1099 (s),
1058 (m), 1023 (s), 931 (s), 901 (m), 846 (s), 793 (s), 758 (s), 725 (s),
696 (s), 635 (m), 525 (m), 456 (s); Anal. calcd. for C70H92Fe2N4P2
(1163.2): C 72.3, H 8.0, N 4.8; found: C 71.8, H 8.3, N 4.6.
Synthesis of [((NacNac)Ni)2(l4-(PPh)2)] 5. Toluene (5 mL)
Synthesis of (NacNac)Fe(g2-CH2CPh2) 3. Toluene (15 mL)
was added to the mixture of ((NacNac)Fe(l-Cl)2)Li(THF)2
(1.392 g, 2.0 mmol) and K/Na alloy (0.063 g K, 1.6 mmol;
0.018 g Na, 0.8 mmol) at room temperature. 1,1-Diphenylethylene
(0.36 g, 2.0 mmol) was added to the mixture, and then stirring
was continued for one week. After filtration and subsequent
concentration (to 5 mL) in vacuo, the resulting green solution was
3
3
was added to the mixture of ((NacNac)Ni)2(l-g -g -C6H5Me)
(0.208 g, 0.10 mmol) and P5Ph5 (0.044 g, 0.081 mmol) at 25 ◦C. The
resulting mixture was stirred for overnight. After concentrati◦on
in vacuo, the resulting deep brown solution was kept at −35 C
for three days to isolate dark purple crystals of 5·1.5C7H8. Yield
0.14 g (54%). IR (Nujol, cm−1): 1920 (w), 1858 (w), 1794 (w),
1728 (s), 1623 (w), 1580 (w), 1525 (s), 1489 (s), 1463 (s0, 1432 (s),
1398 (m), 1383 (s), 1368 (m), 1311 (s), 1275 (m), 1253 (m), 1176
(m), 1124 (m), 1072 (m), 1058 (w), 1040 (w), 1025 (m), 961 (m),
934 (m), 855 (m), 794 (m), 762 (m), 750 (m), 736 (s), 693 (s), 642
◦
kept at −35 C for a week to isolate green crystals of 3 (0.72 g).
After concentration of the filtrate to 3 mL, the solution was kept
at −35 ◦C for three days and an additional crop of 3 (0.21 g) was
obtained. Yield 0.93 g (71%). IR (Nujol, cm−1): 1942 (w), 1918 (w),
1884 (w), 1858 (w), 1796 (w), 1654 (w), 1621 (w), 1592 (m), 1526 (s),
1494 (s), 1459 (s), 1386 (s), 1314 (s), 1259 (s), 1175 (s), 1101 (s), 1053
(m), 1024 (s), 931 (s), 898 (m), 857 (s), 792 (s), 758 (s), 632 (m), 588
(w), 560 (w), 525 (w), 482 (w), 449 (m); Anal. calcd. for C43H53FeN2
(653.8): C 79.0, H 8.2, N 4.3; found: C 78.9, H 8.5, N 4.4.
1
(w), 598 (w), 552 (w), 529 (w) 465 (m); H NMR: 7.15–6.26 (m,
PhMe, PhP and Ar), 5.44 (sept, 3JHH = 7 Hz, 2 H, CHMe2), 4.93
(s, 2 H, c -CH), 4.65 (sept, 3JHH = 7 Hz, 2 H, CHMe2), 4.30 (sept,
3JHH = 7 Hz, 2 H, CHMe2), 3.02 (d, 3JHH = 7 Hz, 6 H, CHMe2),
3
2.69 (sept, JHH = 7 Hz, 2 H, CHMe2), 2.11 (s, PhMe), 1.83 (d,
3
3JHH = 7 Hz, 6 H, CHMe2), 1.66, 1.65 (dd, JHH = 7 Hz, 12 H,
Synthesis of [(NacNac)Fe(l2-PPh)]2 4. Method A: PhPH2
(0.022 g, 0.20 mmol) was added to 3 (0.131 g, 0.20 mmol) in toluene
(5 mL) at 25 ◦C. The resulting solution was stirred overnight.
After concentrati◦on in vacuo, the resulting deep brown solution
was kept at −35 C for three days to isolate dark red crystals of
4. Yield 0.09 g (77%). Method B: Toluene (15 mL) was added to
the mixture of [(NacNac)Fe(l-Cl)]2 (1.392 g, 2.0 mmol) and K/Na
alloy (0.063 g K, 1.6 mmol; 0.018 g Na, 0.8 mmol) at 25 ◦C. Ph2PH
(0.372 g, 2.0 mmol) was added to the mixture, and then stirring
CHMe2), 1.57 (s, 6 H, CMe), 1.25 (s, 6 H, CMe), 1.13 (d, 3JHH
=
7 Hz, 6 H, CHMe2), 1.07 (d, 3JHH = 7 Hz, 6 H, CHMe2), 0.98 (d,
3JHH = 7 Hz, 6 H, CHMe2), 0.16 (d, 3JHH = 7 Hz, 6 H, CHMe2);
13C NMR: 160.9, 160.8 (NC), 154.7, 149.7, 144.1, 143.7, 142.5,
141.8, 126.2, 126.0, 125.9, 125.0, 123.9, 123.6 (Ar), 135.1, 127.2,
126.7 (Ph), 103.6 (c-C), 30.0, 29.5, 29.2, 28.4 (CHMe2), 27.4, 26.8,
25.7, 25.7, 25.4, 25.3, 24.8, 24.1 (CHMe2), 23.6, 23.4 (NCMe); 31
P
NMR: −71.8; Anal. calcd. for C80.5H104N4Ni2P2 (1307.1): C 74.0,
H 8.0, N 4.3; found: C 73.8, H 7.9, N 4.3.
Table 1 Crystallographic data
Formula
1
2
3
4·0.5C7H8
5·1.5C7H8
Formula
C35H48N2NiP
586.43
Orthorhombic
15.6612(18)
16.3201(19)
26.832(3)
C41H52N2NiP
662.53
C43H53FeN2
653.72
Monoclinic
11.970(4)
22.830(8)
13.765(5)
97.209(9)
3732(2)
P21/n
C38.5H50FeN2P
627.63
C80.5H103.5N4Ni2P2
1306.53
Monoclinic
23.028(6)
13.781(4)
24.031(7)
106.742(8)
7303(4)
P21/n
Formula weight
Crystal system
Monoclinic
13.3110(16)
20.471(2)
14.5076(17)
101.689(2)
3871.2(8)
P21/n
Monoclinic
13.1127(6)
14.2879(7)
19.5668(9)
92.8560(10)
3661.3(3)
P21/n
1.055
4
0.477
17870
˚
a/A
˚
b/A
˚
c/A
b/◦
3
˚
Volume/A
Space group
6858.1(14)
Pbca
8
1.136
0.636
62484
6036
D
calc/g cm−3
4
4
1.188
Z
1.137
0.571
36847
6799
418
0.0649
0.1504
1.028
1.163
0.435
17836
5380
4
Abs. coeff., l/mm−1
0.604
15842
9532
806
0.0803
0.1813
0.905
Reflections
2
2
Data Fo > 3r(Fo
)
5262
374
0.0486
0.1179
Parameters
354
417
Ra
Rw
0.0633
0.1411
1.055
0.0397
0.0983
1.019
b
Goodness of Fit
0.905
◦
2
2
1/2
a Data collected at 20 C with Mo Ka radiation (k = 0.71069 A), R = R(Fo − Fc)/RFo. b Rw = {R[w(Fo − Fc 2]/R[w(Fo)2]}
.
˚
)
1142 | Dalton Trans., 2006, 1141–1146
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X-Ray data collection and reduction
Crystals were manipulated and mounted in capillaries in a
glove box, thus maintaining a dry, O2-free environment for each
crystal. Diffraction experiments were performed on a Siemens
SMART System CCD diffractometer. The data were collected in
a hemisphere of data in 1329 frames with 10 s exposure times.
The observed extinctions were consistent with the space groups in
each case. The data sets were collected (4.5◦ < 2h < 45–50.0◦). A
measure of decay was obtained by re-collecting the first 50 frames
of each data set. The intensities of reflections within these frames
showed no statistically significant change over the duration of the
data collections. The data were processed using the SAINT and
XPREP processing packages. An empirical absorption correction
based on redundant data was applied to each data set. Subsequent
solution and refinement was performed using the SHELXTL
solution package.
3
3
Scheme 1 Reactions of ((NacNac)Ni)2(l-g -g -C6H5Me).
Structure solution and refinement
Non-hydrogen atomic scattering factors were taken from the
literature tabulations.24 The heavy atom positions were determined
using direct methods employing the SHELXTL direct methods
routine. The remaining non-hydrogen atoms were located from
successive difference Fourier map calculations. The refinements
were carried out by using full-matrix least squares techniques on
F2, minimizing the function w(|Fo| − |Fc|)2 where the weight w
is defined as 4Fo2/2r (Fo2) and Fo and Fc are the observed and
calculated structure factor amplitudes. In the final cycles of each
refinement, all non-hydrogen atoms were assigned anisotropic
temperature factors in the absence of disorder or insufficient data.
In the latter cases, atoms were treated isotropically. In the case of
2, the phosphorus position was partially disordered and modeled
accordingly. C–H atom positions were calculated and allowed to
ride on the carbon to which they are bonded, assuming a C–H
Fig. 1 EPR spectrum of 2 in toluene at −78 ◦C.
˚
bond length of 0.95 A. H-atom temperature factors were fixed at
1.10 times the isotropic temperature factor of the C-atom to which
they are bonded. The H-atom contributions were calculated, but
not refined. The locations of the largest peaks in the final difference
Fourier map calculation as well as the magnitude of the residual
electron densities in each case were of no chemical significance.
Additional details are provided in the supplementary data.
Fig. 2 ORTEP drawing of 1; 30% thermal ellipsoids are shown. All except
˚
the P–H hydrogen atoms are omitted for clarity. Distances (A), angles
(◦): Ni(1)–N(2) 1.871(3), Ni(1)–N(1) 1.912(4), Ni(1)–P(1) 2.1596(17),
N(2)–Ni(1)–N(1) 97.24(16), N(2)–Ni(1)–P(1) 152.76(12), N(1)–Ni(1)–P(1)
109.98(12).
of 1 the data confirmed the formulation as the Ni(I)–phosphine
adduct (NacNac)Ni(PH2Ph) (Fig. 2). The b-diketiminato chelate
Results and discussion
˚
We have previously reported that tertiary phosphines react
ring results in Ni–N bond distances of 1.871(3) A and 1.912(4)
˚
◦
3
3
with ((NacNac)Ni)2(l-g -g -C6H5Me) to form a b-diketiminato-
Ni(I) tertiary phosphine adducts in a straightforward manner.22
In probing the possibility of P–H bond activation, the cor-
A, with a bite angle of 97.21(16) . The Ni–P bond distance is
2.1596(17) A. The geometry at Ni is distorted from trigonal
˚
planar as the N–Ni–P angles are 152.76(12)◦ and 109.98(12)◦.
This almost “T-shaped” geometry is similar to that previously
reported for the compound (NacNac)Ni(NCPh) consistent with
strong r-donation into the SOMO of b1 symmetry.22 In the case of
2, the analogous formulation (NacNac)Ni(PHPh2) was confirmed
by crystallography (Fig. 3) although disorder in the phosphine
phenyl ring positions was observed. The structural parameters in
3
3
responding reactions of ((NacNac)Ni)2(l-g -g -C6H5Me) with
primary and secondary phosphines were investigated. Reaction of
3
3
((NacNac)Ni)2(l-g -g -C6H5Me) with PH2Ph or PHPh2 proceeds
in a facile manner to afford the yellow products 1 and 2 in 83% and
75% yield, respectively (Scheme 1). These compounds exhibit solu-
tion EPR spectra that are broad signals with g values of 2.195 and
2.196, respectively (Fig. 1). At −78 ◦C, the frozen solution spectra
of these compounds are similar (Fig. 1), exhibiting three signals
with g values of 2.37, 2.27 and 2.13. Single crystal X-ray crystal-
lographic studies were performed for both products. In the case
˚
2 are similar to those in 1 with Ni–N distances of 1.884(4) A and
1.919(4) A, an N–Ni–N angle of 97.35(17) . The Ni–P distance in
2 (2.1824(18) A) is slightly longer than that in 1 and those recently
reported Ni–P distances for (NacNac)Ni(PCy3) (2.2786(8) A) and
◦
˚
˚
˚
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Reaction of 3 with PH2Ph proceeds in a facile manner with
the liberation of 1,1-diphenylethylene and a gas presumed to be
H2. The product is formulated as the Fe(III) dimer formulated as
[(NacNac)Fe(l2-PPh)]2 4 (Scheme 2) based on X-ray data (Fig. 5).
This dimeric compound is a twofold symmetric product in which
two phosphinidene units bridge two (NacNac)Fe centers. The
geometry about the Fe atoms is pseudo-tetrahedral with Fe–N
˚
˚
bond lengths of 2.012(3) A and 2.015(3) A. The Fe–P distances
˚
˚
are found to be 2.4530(11) A and 2.4599(11) A. The b-diketiminato
ligand bite angle in 4 is 94.83(12)◦ which is slightly smaller than
that in 3 presumably a result of the dimeric nature of 4. The
N–Fe–P angles vary from 115.54(9)◦ to 135.53(10)◦ while the
P–Fe–P angle is only 76.64(4)◦. The Fe2P2 core is planar while
the geometry about the bridging P atoms is almost planar with
the sum of the angles about P totaling 356.2◦. An alternative
preparation of 4 was uncovered in the reaction of ((NacNac)Fe(l-
Cl)2)Li(THF)2 with PHPh2 and Na/K. This reaction proceeds
with loss of benzene. Proposed mechanisms for the formation of 4
are shown (Scheme 2) although the proposed intermediates have
not been detected spectroscopically.
Fig. 3 ORTEP drawing of 2 (the more abundant orientation of the
disordered P position is shown); 30% thermal ellipsoids are shown. All
˚
except the P–H hydrogen atoms are omitted for clarity. Distances (A), an-
gles (◦): Ni(1)–N(2) 1.884(4), Ni(1)–N(1) 1.919(4), Ni(1)–P(1) 2.1824(18).
N(2)–Ni(1)–N(1) 97.35(17), N(2)–Ni(1)–P(1) 148.45(14), N(1)–Ni(1)–P(1)
112.74(13).
22
˚
(NacNac)Ni(Ph2PCH2PPh2) (2.2150(9) A). These variations in
Ni–P distances are consistent with the phosphine basicity.
In order to pursue related reactions with Fe(I), the complex
2
(NacNac)Fe(g -CH2CPh2) 3 was prepared and characterized.
Reduction of [(NacNac)Fe(l-Cl)]2 with Na/K in the presence of
CH2CPh2 gave 3 in 67% isolated yield. A crystallographic study of
3 (Fig. 4) revealed the severely distorted planar geometry about Fe
˚
˚
with Fe–N bond lengths of 1.9669(19) A and 2.0014(18) A. The
NacNac chelate bite angle is typical at 95.08(8)◦, while the N–Fe–
C angles are 166.58(8)◦, 98.04(8)◦, 126.55(8)◦ and 138.37(8)◦. The
variation in these angles is consistent with the steric congestion
generated by interaction of the olefin and the NacNac ligand. The
˚
˚
Fe–C distances were found to be 1.995(2) A and 2.089(2) A, with
the latter longer distance corresponding to the substituted carbon
of the olefin. The bound olefin gives rise to a C–C ◦bond distance
Scheme 2 Proposed mechanisms of formation of 4.
ꢀ
˚
of 1.412(3) A, while the C–Fe–C angle is 40.38(9) . While these
parameters suggest some degree of back-bonding from the metal
=
to the C C p* orbital, this species is best viewed as a Fe(I)–olefin
complex. This view is further substantiated by the reactivity of 3
(vide infra).
Fig. 5 ORTEP drawing of 4; 30% thermal ellipsoids are shown. Hydrogen
◦
˚
atoms are omitted for clarity. Distances (A), angles ( ): Fe(1)–N(2)
2.012(3), Fe(1)–N(1) 2.015(3), Fe(1)–P(1) 2.4530(11), Fe(1)–P(1)
2.4599(11), N(2)–Fe(1)–N(1) 94.83(12), N(2)–Fe(1)–P(1) 115.54(9),
N(1)–Fe(1)–P(1) 119.84(9), N(2)–Fe(1)–P(1)ꢀ 135.53(9), N(1)–Fe(1)–P(1)ꢀ
116.57(9), P(1)–Fe(1)–P(1)ꢀ 76.64(4), Fe(1)–P(1)–Fe(1)ꢀ 103.36(4).
Fig. 4 ORTEP drawing of 3; 30% thermal ellipsoids are shown.
Hydrogen atoms are omitted for clarity. Distances (A), angles ( ):
◦
˚
Fe(1)–N(1) 1.9669(19), Fe(1)–C(30) 1.995(2), Fe(1)–N(2) 2.0014(18),
Fe(1)–C(31) 2.089(2), C(30)–C(31) 1.412(3), N(1)–Fe(1)–C(30) 166.58(8),
N(1)–Fe(1)–N(2) 95.08(8), C(30)–Fe(1)–N(2) 98.04(8), N(1)–Fe(1)–C(31)
126.55(8), C(30)–Fe(1)–C(31) 40.38(9), N(2)–Fe(1)–C(31) 138.37(8),
C(31)–C(30)–Fe(1) 73.36(13), C(30)–C(31)–Fe(1) 66.25(12).
The structure of 4 is an example of a dimeric phosphinidene
bridged dimer. While large number of Fe-base phosphidene
clusters25–28 have been characterized, dimers are less common.29
1144 | Dalton Trans., 2006, 1141–1146
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The species [[Fe(CO)3[POC6H2(CMe3)2Me]2] reported by Power
[Ni12Cl2(PPh)2(P2Ph2)4(PHPh)8] contains both bridging l4-PPh
and l6-P2Ph2 ligands.32 In the context of the well established
analogy between the chemistry of P and C, compound 5 appears to
provide the first structural demonstration of the analogy between
a (l4-(PPh)2) unit and that of l4-acetylenes.
et al.30 was the first dimeric Fe-phosphinidene reported and the
˚
˚
Fe–P bonds were found to be 2.202(1) A and 2.112(1) A, much
shorter than those in 4. It is noteworthy that Power also found
˚
a P–P distance of 2.367(2) A implying some P–P interaction,
but described the dimer in terms of an isolobal analog of
cyclobutadiene.
The synthesis of 1 and 2 supports the view that the initial
interaction of phosphine with (NacNac)Ni(I) involves simple
coordination. In both preparations of 4, the reactions are thought
to proceed via oxidation addition of P–H to Fe(I) affording
phosphido-hydride intermediates. In the reactions of PH2Ph and
PHPh2, loss of H2 and benzene, respectively, would lead to the
monomeric phosphinidene complex that dimerizes rapidly to
give 4. Similar mechanistic routes to phosphinidene complexes
involving P–H oxidative addition and reductive eliminations have
been described for several metals including Zr14 and Ti.36 The
oxidative addition of P–H bonds to (NacNac)Fe(I) and simple
coordination to (NacNac)Ni(I) is consistent with the abundance of
Fe(III) species and paucity of Ni(III) compounds. This also suggests
that the related oxidation of Ni(I) by P5Ph5 to the Ni(II) species
5 proceeds via an electron transfer process leading to P–P bond
cleavage although the details of the mechanism remain unknown.
The electrochemical properties of these compounds were probed
by cyclic voltammetric experiments using CH2Cl2 as the solvent
with [Bu4N][PF6] as the supporting electrolyte. Under these
In an attempt to probe the oxidative reactivity of the Ni(I)
3
3
species, the reaction of ((NacNac)Ni)2 (l-g -g -C6H5Me) with
P5Ph5 was examined. The resulting dark purple product 5 is
obtained in 54% yield. This diamagnetic compound exhibits a
1
1
31P{ H} resonance at −71.8 ppm while the H NMR spectrum
reveals resonances attributable to the b-diketiminato ligand as
well as phenyl substituents on P. These data together with
X-ray crystallography are consistent with a formulation of 5
as [((NacNac)Ni)2(l4-(PPh)2)] (Fig. 6). This bimetallic complex
contains two (NacNac)Ni units bridged by a (PPh)2 fragment.
As such, 5 formally contains two Ni(II) centers. In addition the
geometries about the Ni centers are distorted from pseudo-square
planar as the NiN2 and NiP2 planes are twisted with respect to each
other forming angles of 29.4◦ and 28.3◦ for the two Ni centers. The
two NiP2 planes are oriented at an angle of 130.8◦, thus providing
the bent nature of the molecule. The Ni–N bond distances fall in
˚
˚
the range from 1.872(7) A to 1.929(7) A. The chelate bite angles
vary slightly at 95.8(3)◦ and 96.7(3)◦. The Ni–P bond lengths
conditions, compound 1 exhibits an irreversible oxidation at EPa
=
˚
alternate “short” and “long” bonds averaging 2.237(5) A and
0.023V versus SCE. This is attributed to a Ni(I)/Ni(II) redox
couple. In addition, 1 also undergoes further ireversible oxidation
above 0.85 V attributed to the Ni(II)/Ni(III) redox couple. The
irreversible redox chemistry suggests changes to the coordination
number upon oxidation, which could be further complicated by
ligand redistribution.
˚
2.266(5) A, respectively, consistent with r-bond and r-donation
˚
interactions between P and Ni. The P–P bond in 5 is 2.125(3) A,
resulting in P–Ni–P angles of 56.41(9)◦ and 56.19(9)◦.
In contrast, the Fe compound 3, while unstable in CH2Cl2,
exhibits a quasi-reversible Fe(I)/Fe(II) couple at EPa = 0.060 V
versus SCE in THF. The peak-to-peak separation is rather large at
290 mV, suggesting some structural perturbation upon oxidation
of 3. This view is consistent with the pseudo-planar geometry of
3 and the known pseudo-tetrahedral geometry of (NacNac)Fe(II)
species.23
Compound 4 showed irreversible reductions at −0.43 V and
−1.64 V versus SCE in CH2Cl2. In contrast, compound 5 shows a
reversible oxidation at 0.445 V versus SCE (Fig. 7). The peak-to-
peak separation of 60 mV is consistent with a one electron process.
Fig. 6 ORTEP drawing of 5; 30% thermal ellipsoids are shown. Hydrog◦en
˚
atoms and toluene solvates are omitted for clarity. Distances (A), angles ( ):
Ni(1)–N(1) 1.872(7), Ni(1)–N(2) 1.922(6), Ni(1)–P(1) 2.233(2), Ni(1)–P(2)
2.262(2), Ni(2)–N(3) 1.911(6), Ni(2)–N(4) 1.929(7), Ni(2)–P(2) 2.242(2),
Ni(2)–P(1) 2.270(2), P(1)–P(2) 2.125(3), N(1)–Ni(1)–N(2) 95.8(3),
N(1)–Ni(1)–P(1) 153.0(2), N(2)–Ni(1)–P(1) 104.2(2), N(1)–Ni(1)–P(2)
108.6(2), N(2)–Ni(1)–P(2) 153.9(2), P(1)–Ni(1)–P(2) 56.41(9), N(3)–Ni(2)–
N(4) 96.7(3), N(3)–Ni(2)–P(2) 103.8(2), N(4)–Ni(2)–P(2) 153.7(2), N(3)–
Ni(2)–P(1) 154.0(2), N(4)–Ni(2)–P(1) 107.7(3), P(2)–Ni(2)–P(1) 56.19(9),
P(2)–P(1)–Ni(1) 62.50(9), P(2)–P(1)–Ni(2) 61.24(9), P(1)–P(2)–Ni(2)
62.50(9), P(1)–P(2)–Ni(1) 61.09(8), Ni(1)–P(1)–Ni(2) 106.61(10), Ni(2)–
P(2)–Ni(1) 106.55(10).
Previous literature described Ni clusters containing bridg-
ing PR units31–33 as well as complexes containing terminal
Fig. 7 Cyclic voltammogram of 5 in CH2Cl2 using [Bu4N][PF6] as the
supporting electrolyte and a scan rate of 100 mV s−1. Potentials are
referenced to SCE.
Ni PR units.34,35 It appears that 5 is a rare example of a compound
=
containing a (l4-(PPh)2) unit although it is noted that the cluster
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Simon-Manso and Kubiak have reported a similar potential for the
one-electron oxidation of the Ni(I)–Ni(I) dimer [Ni2(l2-PPh2)(l2-
PPh2NHPPh2)2(CNR)2]BPh4.37 Thus, the electrochemical behav-
ior observed for 5 is attributed to the reversible formation of the
mixed valent Ni(I)/Ni(II) species [((NacNac)Ni)2(l4-(PPh)2)]−.
In summary, (NacNac)Ni(I) complexes form three coordinate
complexes with both primary and secondary phosphines. In
contrast, reaction of Fe(I) analogs with primary and secondary
phosphines result in P–H and P–C bond activations affording the
phosphinidene dimer 4. Nonetheless, the Ni(I) species does effect
P–P activation in the reaction with P5Ph5 to give the diphosphine
bridged complex 5. The impact of ligand perturbations on these
P–H, P–C and P–P activations continues to be the subject of study
in our laboratories.
14 D. W. Stephan, Angew. Chem., Int. Ed., 2000, 39, 315.
15 M. A. Zhuravel, N. S. Grewal, D. S. Glueck, K.-C. Lam and A. L.
Rheingold, Organometallics, 2000, 19, 2882.
16 I. V. Kourkine, M. D. Sargent and D. S. Glueck, Organometallics, 1998,
17, 125.
17 D. K. Wicht, I. V. Kourkine, B. M. Lew, J. M. Nthenge and D. S.
Glueck, J. Am. Chem. Soc., 1997, 119, 5039.
18 D. K. Wicht, I. V. Kourkine, I. Kovacik, D. S. Glueck, T. E. Concolino,
G. P. A. Yap, C. D. Incarvito and A. L. Rheingold, Organometallics,
1999, 18, 5381.
19 I. Kovacik, D. K. Wicht, N. S. Grewal, D. S. Glueck, C. D. Incarvito,
I. A. Guzei and A. L. Rheingold, Organometallics, 2000, 19, 950.
20 M. Stradiotto, K. L. Fujdala and T. D. Tilley, Helv. Chim. Acta, 2001,
84, 2958.
21 V. P. W. Bohm and M. Brookhart, Angew. Chem., Int. Ed., 2001, 40,
4694.
22 G. Bai, P. Wei and D. W. Stephan, Organometallics, 2005, 24, 0000.
23 J. M. Smith, R. J. Lachicotte and P. L. Holland, Chem. Commun., 2001,
1542.
CCDC reference numbers 284029–284033.
24 D. T. Cromer and J. B. Mann, Acta Crystallogr., Sect. A: Cryst. Phys.,
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b513892b
Diffr., Theor. Gen., 1968, 24, 321.
25 M. T. Bautista, P. S. White and C. K. Schauer, J. Am. Chem. Soc., 1991,
113, 8963.
26 M. Castiglioni, R. Giordano and E. Sappa, J. Organomet. Chem., 1991,
407, 377.
27 A. M. Arif, A. H. Cowley, M. Pakulski, M. A. Pearsall, W. Clegg,
N. C. Norman and A. G. Orpen, J. Chem. Soc., Dalton Trans., 1988,
2713.
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1146 | Dalton Trans., 2006, 1141–1146
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The Royal Society of Chemistry 2006
©