Platinum(II) hydrazido complexes

Article abstract of DOI:10.1021/ic001432d

Reaction of 1,2-dimethylhydrazine with the platinum hydroxo complex [(dppp)Pt(μ-OH)]₂(BF₄)₂ gives the bridging 1,2-dimethylhydrazido(-2) product [(dppp)₂Pt₂ (μ-η²:η²-MeNNMe)] (BF

Full text of DOI:10.1021/ic001432d

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4016
Inorg. Chem. 2001, 40, 4016-4021
Platinum(II) Hydrazido Complexes
Aibing Xia and Paul R. Sharp*
Department of Chemistry, University of Missouri, 125 Chemistry, Columbia, Missouri 65211
ReceiVed December 20, 2000
Reaction of 1,2-dimethylhydrazine with the platinum hydroxo complex [(dppp)Pt(µ-OH)]2(BF4)2 gives the bridging
1,2-dimethylhydrazido(-2) product [(dppp)2Pt2(µ-η2:η2-MeNNMe)](BF4)2 1. Crystals of 1‚CH2Cl2 from CH2-
Cl2/Et2O are monoclinic (C/2) with a ) 19.690(1), b ) 18.886(1), c ) 17.170 (1) Å, and â ) 92.111(1)°. Treatment
of [(dppp)Pt(µ-OH)]2(OTf)2 with 1,1-dimethylhydrazine gives [(dppp)2Pt2(µ-OH)(µ-NHNMe2)](OTf)2 2. Crystals
of 2‚CH2Cl2 from CH2Cl2/Et2O are triclinic (P-1) with a ) 12.910 (3), b ) 13.927(3), c ) 17.5872 (3) Å, R )
87.121(3), â ) 89.997(4), and γ ) 84.728(3)°. Reaction of [(dppp)Pt(µ-OH)]2(OTf)2 with 1 equiv of
phenylhydrazine in CH2Cl2 gives [(dppp)2Pt2(µ-OH)(µ-NHNHPh)](OTf)2 3. Two equivalents of phenylhydrazine
with [(dppp)Pt(µ-OH)]2(X)2 gives [(dppp)Pt(µ-NHNHPh)]2(X)2 4 (X ) BF4, OTf). Crystals of 3‚ClCH2CH2Cl
from ClCH2CH2Cl/iPr2O are monoclinic (P21/n) with a ) 20.990(2), b ) 13.098(1), c ) 25.773 (2) Å, and â )
112.944(2)°. Crystals of 4(X ) BF4)‚ClCH2CH2Cl.2(tBuOMe) from ClCH2CH2Cl/tBuOMe are monoclinic (C2/
m) with a ) 30.508(1), b ) 15.203(1), c ) 19.049 (1) Å, and â ) 118.505(2)°.
Introduction
In previous work we showed that the oxo complex [(LAu)3-
(µ-O)]+ (L ) a phosphine) is an excellent reagent for the
Transition metal complexes containing metal bonded N2 units
are important in dinitrogen activation and reduction. As a result,
N2 coordination chemistry is of great interest to chemists.1-9
Hydrazido metal complexes are critical models for intermediates
in dinitrogen reduction. The crystal structure determination of
the nitrogenase FeMo cofactor has revealed an Fe7MoS9
cluster10,11 at the active center where dinitrogen coordinates and
is reduced. With the likely involvement of multimetal center
dinitrogen bonding to this cluster, both initially and during
dinitrogen reduction,12-15 polymetallic hydrazido complexes
have taken on a new importance in dinitrogen reduction
modeling. While there are a number of known polymetallic
hydrazido complexes that may serve as models for nitrogenase
dinitrogen reduction, the bulk of these involve early transition
metal systems. Very few complexes past group seven are known,
yet late transition metal complexes may reveal new bonding
modes to consider in dinitrogen reduction.16
formation of complexes with multisite Au-N bonding and that
the reaction of the oxo complex with hydrazines yields a series
of these complexes. The type of complex isolated depends on
the hydrazine substitution. With unsubstituted hydrazine, the
first group 11 dinitrogen complexes [(LAu)6(µ-N2)]2+ were
obtained,16-18 while with substituted hydrazines either the
trimetallic hydrazido complexes,17-19 [(LAu)3(µ-NNR2)]+ or
rearranged semidine complexes20 [(LAu)3(µ-NC6H4NHPh)]+,
were isolated. Similar exchange reactions with the platinum
hydroxo complexes [L2Pt(µ-OH)]22+ (L2 ) a bidentate diphos-
phine) and hydrazine yielded the dimetallic dihydrazido com-
2+ 21
plexes [L2Pt(µ-NHNH2)]2
.
Given the scarcity of late tran-
sition metal polymetallic hydrazido complexes, and the differences
in the gold oxo hydrazine reaction chemistry with hydrazine
substitution, we have extended our investigation of the platinum
2+
system to reactions of [L2Pt(µ-OH)]2 (L2 ) dppp) with
substituted hydrazines. The formation and characterization of
a bridging side-on 1,2-dimethylhydrazido complex and bridging
end-on 1,1-dimethylhydrazido and phenylhydrazido complexes
are described herein.
*To whom correspondence should be addressed. E-mail: SharpP@
missouri.edu.
(1) Sutton, D. Chem. ReV. 1993, 93, 995-1022.
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145.
Reaction of the platinum hydroxo complex22,23 [(dppp)Pt(µ-
OH)]2(BF4)2 with the symmetric hydrazine 1,2-dimethylhydra-
(5) Hirsch-Kuchma, M.; Nicholson, T.; Davison, A.; Jones, A. G. J. Chem.
Soc., Dalton Trans. 1997, 3189-3192.
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10.1021/ic001432d CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/30/2001

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Platinum(II) Hydrazido Complexes
Inorganic Chemistry, Vol. 40, No. 16, 2001 4017
Table 1. Crystallographic and Data Collection Parameters
formula
C59H60B2F8N2P4Pt2‚
CH2Cl2 (1)
1545.7
C2/c
C58H60F6N2O7P4Pt2S2‚
CH2Cl2 (2)
1674.2
P-1
-100
12.910(3)
13.927(3)
17.587(3)
87.121(3)
89.997(4)
84.728(3)
3144(1)
2
C63H60Cl2.5F6N2O7-
P4Pt2S2C2H4Cl2 (3)
1737.9
P21/n
-100
20.990(2)
13.098(1)
25.773(2)
90
112.944(2)
90
6525(1)
4
C77H91B2Cl2-
F8N4O3P4Pt2 (4)
1879.1
C2/m
fw
space group
T, °C
a, Å
b, Å
c, Å
-100
-100
18.690(1)
18.886(1)
17.170(1)
90
30.508(1)
15.203(5)
19.049(1)
90
R, deg
â, deg
γ, deg
92.111(1)
90
6056(1)
4
118.505(1)
90
7764(1)
4
3
V, Å
Z
d
calc, g/cm3
1.695
4.87
0.71073
0.0397
0.1259
1.768
4.77
0.71073
0.0530
0.1450
1.769
4.62
0.71073
0.0504
0.1310
1.608
3.82
0.71073
0.0478
0.1390
µ, mm-1
λ (Mo KR), Å
R1a
wR2b(obs)
a R1 ) (∑||Fo| - |Fc||)/∑|Fo|. b wR2 ) [(∑w(Fo2 - Fc2)2)/∑w(Fc2)2]1/2, with weight ) 1/[σ2(Fo ) + (xP)2 + yP]; x ) 0.0526, y ) 7.5107 for 1;
2
2
x ) 0.1000, y ) 0 for 2; x ) 0.0735, y ) 0 for 3; x ) 0.0584, y ) 0 for 4; P ) (Fo + 2Fc2)/3.
zine in CH2Cl2 gives a white product, 1. Product 1 is soluble in
DMSO but only slightly soluble in CH2Cl2 and THF. NMR data
indicate the presence of a Pt bound chelated dppp ligand24 and
incorporation of dimethylhydrazine. Integration of the dppp and
the hydrazine methyl group signals indicate a 2-to-1 value
for the dppm-to-dimethylhydrazine ratio. This information and
elemental analysis suggest the identity of 1 as the 1,2-
dimethylhydrazido(-2) complex [(dppp)2Pt2(µ-η2:η2-MeNNMe)]-
(BF4)2 (eq 1).
Figure 1. ORTEP drawing of the cationic portion of [(dppp)2Pt2(µ-
η2:η2-MeNNMe)](BF4)2 1. Here and in the following figures, non-
carbon and non-hydrogen atoms are represented by 50% probability
thermal ellipsoids.
This formulation and the presence of the side-bonded bridging
Table 2. Selected Distances (Å) and Angles (Deg) for
[(dppp)2Pt2(µ-η2:η2-MeNNMe)](BF4)2 1
1,2-dimethylhydrazido ligand is confirmed by an X-ray single-
crystal structure determination (Figure 1). An abbreviated
summary of crystal data collection and processing is given in
Table 1. Selected bond distances and angles are listed in Table
2. The structure shows a square-planar edge-shared Pt dimer.
Such structures can be planar or folded along the shared edge
depending on factors such as the metal, the ligands, and steric
interactions.25-27 Complex 1 shows a nonplanar structure with
a fold angle of 112.5°. Other aspects of the structure are
discussed below.
In an attempt to reductively cleave its N-N bond, 1 was
treated with Li in THF. This afforded gray Pt metal and the
Pt(0) complex (dppp)2Pt, whose identity was confirmed by an
X-ray single-crystal structure analysis.28 The fate of the di-
methylhydrazido ligand was not determined.
Pt1-Pt1′
3.220(1)
2.089(5)
2.239(2)
1.429(11)
92.69(6)
131.6(4)
111.1(2)
120.8(4)
Pt1-N1
Pt1-P1
N1-C1n
2.039(5)
2.233(2)
1.473(8)
Pt1′-N1
Pt1-P2
N1-N1′
P1-Pt1-P2
Pt1-N1-C1n
N1-Pt1-P1
C1n-N1-N1′
N1-Pt1-N1′
Pt1′-N1-C1n
N1′-Pt1-P2
Pt1-N1-Pt1′
40.4(3)
125.8(4)
115.9(2)
102.5(2)
hydrazine gives the hydrazido(-1) hydroxo complex [(dppp)2Pt2-
(µ-OH)(µ-NHNMe2)](OTf)2, 2 (eq 2).
Treatment of a CH2Cl2 solution of [(dppp)Pt(µ-OH)]2(OTf)2
with 1 equiv of the unsymmetrical hydrazine 1,1-dimethyl-
(24) Garrou, P. E. Chem. ReV. 1981, 81, 229-266.
(25) Summerville, R. H.; Hoffmann, R. J. Am. Chem. Soc. 1976, 98, 7240.
(26) Au´llon, G.; Ujaque, G.; Lledo´s, A.; Alvarez, S.; Alemany, P. Inorg.
Chem. 1998, 37, 804-813.
(27) Au´llon, G.; Ujaque, G.; Lledo´s, A.; Alvarez, S. Chem. Eur. J. 1999,
5, 1391-1410.
(28) Asker, K. A.; Hitchcock, P. B.; Moulding, R. P.; Seddon, K. R. Inorg.
Chem. 1990, 29, 4146-8.
The presence of two different bridging groups is readily
detected in the 31P NMR spectra of 2, which shows two

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4018 Inorganic Chemistry, Vol. 40, No. 16, 2001
Xia and Sharp
overnight leads to loss of all 31P NMR signals and formation
of a black precipitate.
Curious about the facile reaction between 1,1-dimethyl-
hydrazine and CH2Cl2, we investigated two other chlorinated
hydrocarbons. With ClCH2CH2Cl, [Me2N(CH2CH2Cl)NH2]Cl
was obtained. However, NH2NMe2 did not react with o-
dichlorobenzene, even after heating for one week at 160 °C.
Reactions of 1,1-dimethylhydrazine with chlorinated hydrocar-
bons have previously been described in a patent application.32
Reactions of [(dppp)Pt(µ-OH)]22+ with phenylhydrazine fol-
low more expected lines. With 1 equiv of phenylhydrazine,
hydroxo hydrazido(-1) complex [(dppp)2Pt2(µ-OH)(µ-NHNHPh)]-
(OTf)2, 3, is obtained (eq 4) from [(dppp)Pt(µ-OH)]2(OTf)2.
Figure 2. ORTEP drawing of the cationic portion of [(dppp)2Pt2(µ-
OH)(µ-NHNMe2)](OTf)2 2.
Table 3. Selected Distances (Å) and Angles (Deg) for
[(dppp)2Pt2(µ-OH)(µ-NHNMe2)](OTf)2 2
Pt1-Pt2
3.0867(5)
2.105(5)
2.104(4)
2.230(2)
2.208(2)
1.433(9)
92.99(6)
92.35(1)
174.2(1)
168.3(1)
98.35(13)
76.22(17)
94.65(17)
121.9(4)
109.6(5)
Pt1-N1
2.111(5)
2.095(4)
2.258(2)
2.259(2)
1.469(7)
1.458(9)
93.46(6)
94.17(13)
172.4(1)
170.1(1)
96.21(14)
76.15(18)
94.12(20)
112.3(3)
110.4(5)
Pt2-N1
Pt1-O
Pt2-O
Pt1-P1
Pt1-P2
Pt2-P3
Pt2-P4
N1-N2
N2-C1n
N2-C2n
P1-Pt1-P2
P1-Pt1-O
P2-Pt1-O
P1-Pt1-N1
P2-Pt1-N1
O-Pt1-N1
Pt1-O-Pt2
Pt1-N1-N2
N1-N2-C1n
P3-Pt2-P4
P3-Pt2-O
P4-Pt2-O
P3-Pt2-N1
P4-Pt2-N1
O-Pt2-N1
Pt1-N1-Pt2
Pt2-N1-N2
N1-N2-C2n
Two equivalents or excess phenylhydrazine with [(dppp)Pt-
(µ-OH)]2(X)2 gives the dihydrazido(-1) complex, [(dppp)Pt-
(µ-NHNHPh)]2(X)2, 4 (X ) BF4, OTf; eq 5).
phosphorus signals as doublets, each with 195Pt satellites. The
signal with the smaller P-Pt coupling is assigned to the
phosphorus atoms trans to the more strongly donating hydrazido
ligand.29-31 The structure of 2 was determined by X-ray single-
crystal diffraction methods and is shown in Figure 2. An
abbreviated summary of crystal data collection and processing
is given in Table 1. Selected bond distances and angles are listed
in Table 3. Again, the structure is typical of square-planar edge-
shared Pt dimers. Unlike in 1, the hydrazido ligand in 2 is not
side-bonded and bridges through a single nitrogen atom. Details
of the structure are discussed below.
Further reaction of 1,1-dimethylhydrazine in CH2Cl2 with 2
at ambient temperatures did not give the expected second
hydroxo-hydrazido exchange and the bis(1,1-dimethyl-
hydrazido(-1)) complex [(dppp)Pt(µ-NHNMe2)]2(OTf)2. In-
stead, (dppp)PtCl2 was obtained. The source of the chloride ion
in the formation of (dppp)PtCl2 in the reaction of 2 with excess
1,1-dimethylhydrazine in CH2Cl2 (eq 2) is apparently the CH2-
Cl2 solvent. A solution of 1,1-dimethylhydrazine in CH2Cl2
rapidly produces the adduct [Me2N(CH2Cl)NH2]Cl (eq 3), as
determined by NMR analysis and a single-crystal X-ray
diffraction experiment (Supporting Information). Complex 2 did
not react further with excess NH2NMe2 in either THF or
o-dichlorobenzene. Heating 2 in o-dichlorobenzene at 80 °C
The hydroxo hydrazido(-1) complex 3 can also be obtained
by the conproportionation of [(dppp)Pt(µ-OH)]22+ and 4 in CH2-
Cl2 (2 d). The structures of 3 (Figure 3) and 4 (X ) BF4, Figure
4) were determined by single-crystal X-ray diffraction experi-
ments. An abbreviated summary of crystal data collection and
processing is given in Table 1. Selected bond distances and
angles are listed in Tables 4 and 5.
Discussion
The formation of the hydrazido complexes in the above
reactions may be viewed as a deprotonation of the hydrazine
by the basic hydroxo ligands. This approach, the reaction of a
basic ligand complex with hydrazines, has been used in several
other systems for the preparation of transition metal hydrazido
complexes. We have previously used Pt21 and Au17-19 com-
plexes with basic hydroxo or oxo ligands in the formation of
hydrazido complexes. Others have used basic alkyl,33 oxo,34-40
(29) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV. 1973,
10, 335.
(30) Hartley, F. R. The Chemistry of Platinum and Palladium; Appl. Sci.
Publishers: London, 1973.
(31) Shustorovich, E. M.; Porai-Koshits, M. A.; Buslaer, Yu. A. Coord.
Chem. ReV. 1975, 17, 1.
(32) Badische Anilin-&Soda-Fabrik A.-G. Plant Growth Regulators, Neth.
Appl. 6, 516, 589. Chem. Abstr. 1966; 65, 18499d.
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106, 6, 8316-17.
(34) Sun, X.-R.; Huang, J.-S.; Cheung, K.-K.; Che, C.-M. Inorg. Chem.
2000, 39, 820-826.

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Platinum(II) Hydrazido Complexes
Inorganic Chemistry, Vol. 40, No. 16, 2001 4019
Table 4. Selected Distances (Å) and Angles (Deg) for
[(dppp)2Pt2(µ-OH)(µ-NHNHPh)](OTf)2 3
Pt1-Pt2
3.0647(5)
2.108(6)
2.111(5)
2.217(2)
2.222(2)
92.70(8)
93.20(2)
174.0(2)
169.3(2)
97.97(17)
76.12(21)
93.60(21)
112.3(5)
119.6(7)
Pt1-N1
2.105(6)
2.093(5)
2.250(2)
2.240(2)
1.496(10)
91.00(7)
95.74(2)
172.6(1)
171.3(2)
97.50(17)
75.68(21)
93.36(24)
107.3(4)
Pt2-N1
Pt1-O
Pt2-O
Pt1-P1
Pt1-P2
Pt2-P3
Pt2-P4
N1-N2
P1-Pt1-P2
P1-Pt1-O
P2-Pt1-O
P1-Pt1-N1
P2-Pt1-N1
O-Pt1-N1
Pt1-O-Pt2
Pt1-N1-N2
N1-N2-C1
P3-Pt2-P4
P3-Pt2-O
P4-Pt2-O
P3-Pt2-N1
P4-Pt2-N1
O-Pt2-N1
Pt1-N1-Pt2
Pt2-N1-N2
Table 5. Selected Distances (Å) and Angles (Deg) for
[(dppp)Pt(µ-NHNPh)]2(BF4)2 4
Figure 3. ORTEP drawing of the cationic portion of [(dppp)2Pt2(µ-
OH)(µ-NHNHPh)](OTf)2 3.
Pt1-Pt2
3.0687(5)
2.105(5)
2.259(2)
93.13(8)
95.58(15)
169.8(2)
75.3(3)
Pt1-N1
2.110(5)
2.273(2)
1.455(7)
92.85(9)
95.75(16)
170.8(2)
75.5(3)
Pt2-N1
Pt1-P1
Pt2-P2
N1-N2
P1-Pt1-P1′
P1-Pt1-N1
P1-Pt1-N1′
N1′-Pt1-N1
Pt1-N1-Pt2
Pt2-N1-N2
P2-Pt2-P2′
P2-Pt2-N1
P2-Pt2-N1′
N1′-Pt2-N1
Pt1-N1-N2
N1-N2-C1
93.4(2)
108.0(4)
116.9(4)
117.1(5)
Scheme 1
Figure 4. ORTEP drawing of the cationic portion of [(dppp)Pt(µ-
NHNHPh)]2(BF4)2 4.
and amido41 ligand complexes to produce mostly terminal
hydrazido complexes.
One of the notable features of the reactions in the current
study is the product variation with the substituents on the
hydrazine. In our earlier work with unsubstituted hydrazine, the
sole observed products were the dihydrazido complexes [L2Pt-
(µ-NHNH2)]22+, analogous to 4.21 With the substituted hydra-
zines studied here, the mixed hydrazido hydroxo complexes 2
and 3 are observed. This may be explained in steric terms, where
the second substitution of the hydroxo group by the hydrazido
group is slowed (PhHNNH2) or stopped completely (Me2NNH2).
We have previously observed steric inhibition in reactions of
the hydroxo complexes with anilines, where mixed hydroxo-
amido complexes were isolated.21 Driver and Hartwig have
studied hydroxo-amido exchange reactions in related Pd
complexes and have found that these reactions are initiated by
bridge cleavage.42 Scheme 1 illustrates a likely pathway, derived
from Driver and Hartwig’s work, for the hydroxo-hydrazido
exchange reactions in the current Pt system. Possible steric
inhibition in the second hydrazine coordination step is apparent.
More difficult to explain is the formation of the side-bonded
hydrazido complex 1. Two possible pathways for the formation
of 1 are shown in Scheme 2. In path A, the formation of 1 is
preceded by the formation of a hydroxo hydrazido(-1) complex
5 analogous to 3. Sterics would disfavor formation of a
dihydrazido complex. Intermediate hydroxo hydrazido(-1)
complex 5 then needs to eliminate water to form 1. Although
hydroxo hydrazido complex 2 should not be capable of
following this pathway since there is no hydrogen atom available
for elimination, the phenylhydrazido(-1) hydroxo 3 should be
able to follow this same pathway. Yet, 3 is stable, and all
attempts to force 3 to eliminate water and form a side bonded
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