Activation of arylnitroso substrates on a platinum-germylene complex facilitating the formation of new N-C and N-S bonds

Article abstract of DOI:10.1021/ja980888f

The reaction of (Et₃P)₂PtGe[N(SiMe₂)₂]₂ (1) with nitrosobenzene and 2-nitrosotoluene yields (Et₃P)₂-PtN(Ph)OGe[N(siMe₃)₂]₂ (3a) and (Et₃P)₂PtN(o-Tol)OGe[N(SiMe₃)₂]₂ (3b), respectively. The reactivity of 3a with SO₂, H₂CO, CO₂, and PhNCO was explored yielding the five-membered heterocyclic complex (Et₃P)₂- PtS(O)₂N(Ph)OGe[N(SiMe₃)₂]₂ (6a) and the six-membered heterocyclic complexes (Et₃P)2PtOC(H)₂N(Ph)OGe[N(SiMe₃)₂]₂ (7a), (Et₃P)₂PtoC(O)N(Ph)OGe [N(SiMe₃)₂]₂ (8a), and (Et₃P)₂PtN(Ph)C(O)N(Ph)C(O)N(Ph)OGe- [N(SiMe₃)₂]₂ (9a), respectively. The structures of 3a, 6a, 7a, and 9a were determined by single-crystal X-ray diffraction. 3b was observed to react in a fashion similar to 3a as demonstrated by reactions with SO₂ and H₂CO which gave (Et₃P)2PtS(O)₂N(o-Tol)OGe[N(SiMe₃)₂]₂ (6b) and (Et₃P)₂PtOC(H)₂N(o-Tol)OGe[N(SiMe₃)₂]₂ (7b). Complexes 6a and 6b represent the first isolated and characterized examples of metal-stabilized -S(O)₂N-(R)O- fragments, the isoelectronic analogue of an elusive intermediate proposed as the first step in Contact Process for the oxidation of SO₂ by platinum catalysts. As a group, the reactions in this paper demonstrate the cooperative ability of metal-germylenes to activate unsaturated organic substrates and promote their subsequent chemical modification, while avoiding scission of the Pt-Ge bond.

Full text of DOI:10.1021/ja980888f

7484
J. Am. Chem. Soc. 1998, 120, 7484-7492
Activation of Arylnitroso Substrates on a Platinum-Germylene
Complex Facilitating the Formation of New N-C and N-S Bonds
Kyle E. Litz, Jeffrey W. Kampf, and Mark M. Banaszak Holl*
Contribution from the Department of Chemistry, UniVersity of Michigan, Ann Arbor, Michigan 48109-1055
ReceiVed March 16, 1998
Abstract: The reaction of (Et3P)2PtGe[N(SiMe3)2]2 (1) with nitrosobenzene and 2-nitrosotoluene yields (Et3P)2-
PtN(Ph)OGe[N(SiMe3)2]2 (3a) and (Et3P)2PtN(o-Tol)OGe[N(SiMe3)2]2 (3b), respectively. The reactivity of
3a with SO2, H2CO, CO2, and PhNCO was explored yielding the five-membered heterocyclic complex (Et3P)2-
PtS(O)2N(Ph)OGe[N(SiMe3)2]2 (6a) and the six-membered heterocyclic complexes (Et3P)2PtOC(H)2N(Ph)-
OGe[N(SiMe3)2]2 (7a), (Et3P)2PtOC(O)N(Ph)OGe[N(SiMe3)2]2 (8a), and (Et3P)2PtN(Ph)C(O)N(Ph)OGe-
[N(SiMe3)2]2 (9a), respectively. The structures of 3a, 6a, 7a, and 9a were determined by single-crystal X-ray
diffraction. 3b was observed to react in a fashion similar to 3a as demonstrated by reactions with SO2 and
H2CO which gave (Et3P)2PtS(O)2N(o-Tol)OGe[N(SiMe3)2]2 (6b) and (Et3P)2PtOC(H)2N(o-Tol)OGe[N(SiMe3)2]2
(7b). Complexes 6a and 6b represent the first isolated and characterized examples of metal-stabilized -S(O)2N-
(R)O- fragments, the isoelectronic analogue of an elusive intermediate proposed as the first step in Contact
Process for the oxidation of SO2 by platinum catalysts. As a group, the reactions in this paper demonstrate
the cooperative ability of metal-germylenes to activate unsaturated organic substrates and promote their
subsequent chemical modification, while avoiding scission of the Pt-Ge bond.
Introduction
groups is being examined. In this paper, we report the reaction
of nitrosobenzene and 2-nitrosotoluene with 1 generating four-
membered metallacyclic adducts containing an extremely length-
ened N-O bond. Furthermore, a variety of insertion reactions
into the nitroso-adducts have been explored.6 A particularly
interesting insertion of SO2 forms new N-S bonds and leads
to a unique complex related to a key proposed intermediate in
the Contact Process.7 Insertion products of PhNCO, H2CO, and
CO2, leading to new N-C bonds, are also described. These
reactions provide a demonstration that the metal-germylene
nexus can activate unsaturated organic substrates and promote
their further chemical modification.
The germylene ligand binds in a dative sense to electron-
rich late transition metals and maintains the presence of an active
Lewis acid site.1 This combination of properties provides
compelling incentive to explore the ability of the M-Ge nexus
to activate a variety of small molecules and functional groups.
Significant challenges to be overcome in transition metal-
germylene chemistry include (1) irreversible oxidation of the
germylene to a metal bound germyl and (2) uncontrolled M-Ge
bond scission. Group 10 metal-germylene complexes provide
a powerful combination of electronic donor and acceptor orbitals
at a chemically convenient distance of separation. The strongly
basic Pt0 and Ni0 in (Et3P)2PtGe[N(SiMe3)2]2 (1) and (Ph3P)2-
NiGe[N(SiMe3)2]2 (2) are located just 2.30 and 2.21 Å,
respectively, from the Lewis acidic Ge(II) atom.2,3 This
proximate pairing of metal orbitals has been shown to promote
interaction with small molecules, such as CO2, yielding novel
cycloadducts. In addition, reVersible metal-germyl formation
in concert with H2 and CO2 activation, reversible Pt-Ge scission
leading to the formation of bisaminogermane, and catalytic
synthesis of amide germanes have been observed.2,3 A variety
of interesting chemical behavior has been noted in related
M-Ge/Si/Sn systems.4 Of particular relevance to work reported
in this paper, Tilley et al. have recently observed the reversible
cycloaddition of isocyanates on metal-silylene complexes,
[Cp*(PMe3)2RudSiR2]BPh4 (R ) Me, Ph).5
Experimental Section
All manipulations were performed using air-free technique and dry,
deoxygenated solvents. Toluene, hexane, and benzene-d6 were degassed
(4) (a) For example, see: Koe, J. R.; Tobita, H.; Suzuki, T.; Ogino, H.
Organometallics 1992, 11, 150. (b) Koe, J. R.; Tobita, H.; Ogino, H.
Organometallics 1992, 11, 2479. (c) Figge, L. K.; Carroll, P. J.; Berry, D.
H. Angew. Chem., Int. Ed. Engl. 1996, 35, 435. (d) Figge, L. K.; Carroll,
P. J.; Berry, D. H. Organometallics 1996, 15, 209. (e) Reichl, J. A.; Popoff,
C. M.; Gallagher, L. A.; Remsen, E. E.; Berry, D. H. J. Am. Chem. Soc.
1996, 118, 9430. (f) Baines, K. M.; Cooke, J. A.; Vittal, J. J. J. Chem. Soc.
Chem. Commun. 1992, 1484. (g) Toltl, N. P.; Leigh, W. J.; Kollegger, G.
M.; Stibbs, W. G.; Baines, K. M. Organometallics 1996, 15, 3732. (h)
Sharma, H. K.; Cervantes-Lee, F.; Parkanyi, L.; Pannell, K. H. Organo-
metallics 1996, 15, 5, 429. (i) Sharma, S.; Cervantes, J.; Mata-Mata, J. L.;
Brun, M.-C.; Cervantes-Lee, F.; Pannell, K. H. Organometallics 1996, 14,
4269. (j) Sharma, H.; Pannell, K. H. Organometallics 1996, 13, 4946. (k)
Barrau, J.; Rima, G.; Cassano, V.; Satge, J. Inorg. Chim. Acta 1992, 189-
200, 461. (l) Chaubon-Deredempt, M. A.; Escudie, J.; Couret, C. J.
Organomet. Chem. 1994, 467, 37.
(5) Tilley, T. D.; Mitchell, G. P. J. Am. Chem. Soc. 1997, 119, 11236.
(6) Lead references into previous work in this area include (a) Pizzotti,
M.; Porta, F.; Cenini, S.; Demartin, F.; Masciocchi, N. J. Organomet. Chem.
1987, 330, 265. (b) Bellon, P. L.; Cenini, S.; Demartin, F.; Pizzotti, M.;
Porta, F. J. Chem. Soc., Chem. Commun. 1982, 265. (c) Cenini, S.; Porta,
M.; Pizzotti, M.; LaMonica, G. J. Chem. Soc., Chem. Dalton Trans. 1984,
355. (d) Cenini, S.; Porta, F.; Pizzotti, M.; Crotti, C. J. Chem. Soc., Dalton
Trans. 1985, 163. (e) Demartin, F.; Pizzotti, M.; Porta, F. J. Chem. Soc.,
Dalton Trans. 1987, 605.
As part of our exploration of metal-germylene chemistry,
activation and subsequent modification of organic functional
(1) For reviews on germylenes, see: (a) Neumann, W. P. Chem. ReV.
1991, 91, 311-334. (b) Barrau, J.; Escudie, J.; Satge, J. Chem. ReV. 1990,
90, 283-319. (c) Lappert, M. F.; Rowe, R. S. Coord. Chem. ReV. 1990,
100, 267-292. (d) Petz, W. Chem. ReV. 1986, 86, 1019-1047. (e) Tandura,
S. N.; Gurkova, S. N.; Gusev, A. I. Zh. Strukt. Khim. 1990, 31, 154.
(2) Litz, K. E.; Bender, J. B.; Kampf, J. W.; Banaszak Holl, M. M.
Angew. Chem., Int. Ed. Engl. 1997, 36, 496.
(3) Litz, K. E.; Henderson, K. H.; Gourley, R. W.; Banaszak Holl, M.
M. Organometallics 1995, 14, 5008.
(7) For lead references into the area of homogeneous SO2 oxidation,
see: Kubas, G. J. Acc. Chem. Res. 1994, 27, 183.
S0002-7863(98)00888-9 CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/17/1998

Arylnitroso Substrates on a Platinum-Germylene Complex
J. Am. Chem. Soc., Vol. 120, No. 30, 1998 7485
and dried over sodium benzophenone ketyl. Chloroform was degassed
and stored over 4 Å molecular sieves. Chloroform-d was used as
received from Cambridge Isotopes. PhNO, 2-nitrosotoluene, N-
nitrosodimethylamine, 2,4,6-tri-tert-butylnitrosobenzene, paraformal-
dehyde, and dimethylacetylene dicarboxylate (Aldrich Chemical) were
degassed in vacuo and stored under dinitrogen in a drybox. The
following complexes were prepared according to previously published
procedures: (Et3P)2PtGe[N(SiMe3)2]2 (1),3 (Ph3P)2NiGe[N(SiMe3)2]2
(2),2 (Et3P)2PtO2C13O,8 and Ge[N(SiMe3)2]2.9 1H, 13C, and 31P NMR
spectra were obtained in the listed deuterated solvents on a Bruker AM-
360 spectrometer (360.1, 90.6, and 145.8 MHz) and referenced to
residual protons, solvent carbons, and external 85% H3PO4 in D2O,
respectively. IR spectra were recorded on a Nicolet 5DXB as Nujol
mulls or KBr disks. All compounds reported are moisture sensitive to
hydrolysis reactions of the Ge[N(SiMe3)2]2 ligand.
found to be insoluble in diethyl ether and pentane, yet displayed limited
solubility in benzene and toluene; it was quite soluble in chloroform
and THF. 1H NMR (C6D6) δ 0.60 (broad s, 36H, N(SiMe3)2), 0.72
(m, 9H, CH2CH3), 0.83 (m 9H, CH2CH3), 1.82 (m, 6H, CH2CH3), 1.86
(m, 6H, CH2CH3), 6.99 (1H, aromatic), 7.27 (2H, aromatic), 8.12 (2H,
aromatic); 13C NMR (CDCl3) δ 7.19 (s, SiMe3), 8.10 (d, PCH2CH3),
9.18 (d, PCH2CH3), 16.23 (m, PCH2CH3), 20.03 (m, PCH2CH3), 124.16
(s, aromatic), 124.85 (s, aromatic), 127.67 (s, aromatic), 141.78 (s, N-C
aromatic); 31P NMR (CDCl3) δ 7.15 (d w/195Pt satellites, 1JPt-P ) 2025
Hz, 2JP-P ) 22 Hz), -6.48 (d w/195Pt satellites, 1JPt-P ) 2866 Hz, 2JP-P
) 22 Hz); IR (Kbr) 1384 (asym ν-SO2), 1165 (sym ν-SO2); Elemental
analysis for C30H71N3GeO3P2SSi4Pt: C, 36.18, H, 7.19; N, 4.22.
Found: C, 37.65; H, 6.89; N, 3.74.
(Et3P)2PtS(O)2N(o-Tol)OGe[N(SiMe3)2]2 (6b). SO2 (1 equiv) was
condensed from a measured gas bulb into a frozen 0.25 mL C6D6
solution of 3b (60 mg, 0.063 mmol) in an NMR tube fitted with a
Teflon valve. After sealing the tube, the solution was rapidly thawed
resulting in an immediate color change from dark orange to colorless.
Complete conversion to 6b was demonstrated by NMR analysis. 1H
NMR (C6D6) δ 0.48 (s, 9H, N(SiMe3)2), 0.53 (s, 9H, N(SiMe3)2), 0.67
(s, 9H, N(SiMe3)2), 0.81 (s, 9H, N(SiMe3)2), 0.83 (m, 18H, CH2CH3),
1.86 (m, 12H, CH2CH3), 2.90 (s, 3H, tol-CH3), 7.01 (m, 1H, aromatic),
7.16 (s, 1H, aromatic), 7.21 (d, 1H, aromatic); 8.28 (d, 1H, aromatic);
13C NMR (C6D6) δ 6.79 (s, SiMe3), 7.49 (s, SiMe3), 7.69 (d, SiMe3),
7.94 (d, SiMe3), 8.69 (m, PCH2CH3), 16.15 (m, PCH2CH3), 19.80 (m,
PCH2CH3), 20.60 (s, Aromatic-Me), 125.1 (s, aromatic), 126.1 (s,
aromatic), 127.8 (s, aromatic), 130.5 (s, aromatic), other aromatic
carbons too weak to detect at this concentration; 31P NMR (C6D6) δ
8.89 (d w/195Pt satellites, 1JPt-P ) 2042 Hz, 2JP-P ) 23 Hz), -4.14 (d
(Et3P)2PtN(Ph)OGe[N(SiMe3)2]2 (3a). To a stirring, cold (-78 °C)
25 mL toluene solution of 1 (0.01 M) was added 0.025 g (0.24 mmol)
of PhNO via a solids addition tube. The color darkened from yellow
to amber at -50 °C. After 3 h at -11 °C, the dark orange solution
was filtered, and the toluene was removed in vacuo leaving a dark red
oil. Recrystallization from a minimum of cold hexane at -78 °C and
drying in vacuo gave 0.120 g of an orange precipitate (51% isolated
yield). The thermally stable solid was observed to be light sensitive,
decomposing over a period of several days. X-ray quality crystals were
obtained by slow evaporation of a benzene solution. 1H NMR (C6D6)
δ 0.62 (s, 36H, N(SiMe3)2), 0.82 (m, 18H, CH2CH3), 1.49 (m, 6H,
CH2CH3), 1.70 (m, 6H, CH2CH3), 6.63 (1H, aromatic), 7.09 (2H,
aromatic), 7.27 (2H, aromatic); 13C NMR (C6D6) δ 7.54 (s, N(SiMe3)2),
8.31 (d, CH2CH3), 8.97 (d, CH2CH3), 18.24 (m, CH2CH3), 21.30 (m,
CH2CH3), 113.74 (s, aromatic), 115.88 (s, aromatic), 127.73 (s,
aromatic) other is obscured by solvent; 31P NMR (C6D6) δ -9.23 (d
1
2
w/195Pt satellites, JPt-P ) 2757 Hz, JP-P ) 23 Hz); IR (KBr) 1384
cm-1, (ν asym SO2), 1181 cm-1 (ν sym. SO2).
2
1
w/195Pt satellites, JP-P ) 16.8 Hz, JPt-P ) 3021 Hz), 4.44 (d w/195Pt
satellites, 2JP-P ) 16.8 Hz, 1JPt-P ) 1888 Hz). Elemental analysis for
C30H71N3GeOP2PtSi4: C, 38.67, H, 7.68; N, 4.51. Found: C, 38.62,
H, 7.57, N, 4.55.
(Et3P)2PtOC(H2)N(Ph)OGe[N(SiMe3)2]2 (7a). Paraformaldehyde
(71 mg, 0.79 mmol of H6C3O3) was added to a stirring 5 mL C6H6
solution of 3a (210 mg, 0.22 mmol) under argon in a darkened vessel.
After 1 h, filtration from excess unreacted paraformaldehyde followed
by recrystallization from pentane gave 123 mg of a tan powder (58%
isolated yield). 1H NMR (C6D6) δ 0.69 (s, 36H, Si(CH3)3), 0.78 (m,
9H, CH2CH3), 0.88 (m, 9H, CH2CH3), 1.50 (m, 6H, CH2CH3), 1.73
(Et3P)2PtN(o-Tol)OGe[N(SiMe3)2]2 (3b). In the same fashion as
3a, 0.037 g (0.31 mmol) of 2-nitrosotoluene was added to a toluene
solution of 1 (0.250 g, 0.30 mmol) at -78 °C. An amber hue developed
at -10 °C. After stirring for 3 h (11 °C), the solution was filtered,
and the solvent was removed in vacuo leaving a dark red oil.
Recrystallization from a minimum of cold hexane at -78 °C and drying
in vacuo gave 0.118 g (41% isolated yield) of an orange solid. The
thermally stable solid was observed to be light sensitive, decomposing
over a period of several days. 1H NMR (C6D6) δ 0.53 (broad, 18H,
N(SiMe3)2), 0.70 (broad, 18H, N(SiMe3)2), 0.83 (m, 18H, CH2CH3),
1.16 (m, 3H, CH2CH3), 1.30 (m, 3H, CH2CH3), 1.70 (m, 6H, CH2-
CH3), 2.75 (s, 3H, tol-CH3), 6.96 (1H, aromatic), 7.10 (1H, aromatic),
7.18 (1H, aromatic); 7.55 (1H, aromatic); 13C NMR (C6D6) δ 7.91 (s,
N(SiMe3)2), 8.97 (d, CH2CH3), 16.7 (m, CH2CH3), 20.2 (s, tol-CH3)
21.2 (m, CH2CH3), 122.1 (s, aromatic), 123.8 (s, aromatic), 126.7 (s,
aromatic), 130.6 (s, aromatic), 136.0 (aromatic quaternary to methyl),
160 (N-C quaternary aromatic); 31P NMR (C6D6) δ -7.24 (d w/195Pt
4
(m, 6H, CH2CH3), 5.11 (broad d w/195Pt satellites, JP-H ) 6.8 Hz,
3JPt-H ) 56 Hz, 2H, CH2O), 6.90 (1H, aromatic), 7.30 (2H, aromatic),
7.63 (2H, aromatic); 13C NMR (C6D6) δ 153.1 (s, ipso-Ph), 127 (s,
aromatic), 121.8 (s, para-Ph), 119.9 (s, ortho-Ph), 93.3 (s, form) 19.2
(m, CH2CH3), 14.2 (m, CH2CH3), 8.65 (m, CH2CH3), 8.37 (m,
CH2CH3), 7.74 (s, Si(CH3)3); 31P{1H} NMR (C6D6) δ 19.11 (d, w/
1
2
195Pt satellites, JPt-P ) 1859 Hz, JP-P ) 15.8 Hz), -7.5 (d w/195Pt
1
2
satellites, JPt-P ) 3508 Hz, JP-P 15.8 Hz); IR (KBr) 1244 ν(C-O),
899/878/857 cm-1 (vs) ν(Ge/Si-N); Elemental Analysis Calcd for
C31H73GeN3O2P2PtSi4: C, 38.71; H, 7.65; N, 4.37. Found C, 38.32;
H, 7.41; N, 4.08.
(Et3P)2PtOC(H2)N(o-Tol)OGe[N(SiMe3)2]2 (7b). Paraformalde-
hyde (5 mg, 0.16 mmol) was allowed to react with 0.020 g (0.02 mmol)
of 3b in an NMR tube. After 1 h complete conversion to 7b occurred.
1H NMR (C6D6) δ 0.70 (s, 36H, N(SiMe3)2), 0.78 (m, 18H, CH2CH3),
1.50 (m, 6H, CH2CH3), 1.74 (m, 6H, CH2CH3), 2.53 (s, 3H, tol-CH3),
2
1
satellites, JP-P ) 15.4, JPt-P ) 2794 Hz), 8.00 (d w/195Pt satellites,
2JP-P ) 15.1 Hz, 1JPt-P ) 1914 Hz); Elemental analysis for C31H73N3-
GeOP2PtSi4: C, 39.36, H, 7.78; N, 4.44. Found: C, 39.04; H, 7.71;
N, 4.44.
4
3
4.75 (broad d w/195Pt satellites, JP-H ) 8 Hz, JPt-H ) 47 Hz, 2H,
CH2O), 6.98 (m, 1H, aromatic), 7.12 (s, 1H, aromatic), 7.35 (d, 1H,
aromatic); 8.32 (d, 1H, aromatic).
(Et3P)2PtS(O)2N(Ph)OGe[N(SiMe3)2]2 (6a). A 15 mL toluene
solution of 3a (0.142 g, 0.15 mmol) was generated as described above.
SO2 (0.15 mmol) was condensed via a measured gas bulb into the
stirring -78 °C solution of crude 3a causing an immediate color change
to light yellow. The solution was warmed to room temperature over
3 h followed by removal of all volatiles in vacuo. Extraction with a
minimum (0.5 mL) of THF under an inert atmosphere followed by
addition of ∼0.1 mL diethyl ether resulted in large, colorless crystals
of 6 over 24 h. The collected crystals were washed with 2 × 0.5 mL
of diethyl ether leaving 102 mg (66% isolated yield) of 6a. 6a was
(Et3P)2PtOC(O)N(Ph)OGe[N(SiMe3)2]2 (8a). A 10-fold excess of
20% 13CO2/ CO2 was condensed into an NMR tube containing 100 mg
(0.11 mmol) of 3a dissolved in 0.25 mL of C6D6. The solution quickly
lightened from dark orange to light orange within an hour. 1H NMR
(C6D6) δ 0.57 (s, 36H, Si(CH3)3), 0.70 (m, 9H, CH2CH3), 0.90 (m,
9H, CH2CH3), 1.69 (m, 6H, CH2CH3), 1.79 (m, 6H, CH2CH3), 6.95 (t,
para-aromatic), 7.35 (t, meta-Ph), 7.99 (d, ortho-Ph); 13C NMR (C6D6)
δ 161.46 (d, 13CO2 , 3JP-C ) 2.4 Hz), 128.53 (s, aromatic), 124.71 (s,
aromatic), 123.03 (s, aromatic), 122.63 (s, aromatic) 20.07 (m, CH2-
CH3), 14.6 (m, CH2CH3), 9.08 (m, CH2CH3), 8.33 (m, CH2CH3), 7.23
(s, Si(CH3)3); 31P{1H} NMR (C6D6) δ 20.18 (d, w/195Pt satellites, 1JPt-P
(8) Prepared according to the silver (I) carbonate route described:
Hayward, P. J.; Blake, D. M.; Wilkinson, G.; Nyman, C. J. J. Am. Chem.
Soc. 1970, 92, 5873-5878.
(9) Gynane, M. J. S.; Harris, D. H.; Lappert, M. F.; Power, P. P.; Riviere,
P.; Riviere-Baudet, M. J. Chem. Soc., Dalton Trans. 1977, 2004-2009.
2
1
) 1873 Hz, JP-P ) 18.6 Hz), -10.25 (d w/195Pt satellites, JPt-P
)
,
4014 Hz, 2JP-P 17.4 Hz); IR (solution in toluene/NaCl cell; mode, cm-1

7486 J. Am. Chem. Soc., Vol. 120, No. 30, 1998
Litz et al.
Table 1. Summary of Crystallographic Data for 3a, 6a, 7a, and 9a
compound
3a
6a
7a
9a
empirical formula
formula weight
temperature
C30H71GeN3OP2PtSi4
931.87
178(2) K
C33H70GeN3O3P2PtSSi4‚3C6H6 C34H76GeN3O2P2PtSi4‚C6H6
C46H65GeN4O2P2PtSi4‚1.5C6H6
1265.30
1079.07
1253.17
158(2) K
158(2) K
153(2) K
wavelength
0.71073 Å
0.71073 Å
0.71073 Å
0.71073 Å
crystal system
space group
unit cell dimensions
monoclinic
C2/c
orthorhombic
Pna21
triclinic
P1h
monoclinic
P21/c
a ) 42.928(3) Å
b ) 11.3730(10) Å
c ) 19.3500(10) Å
R ) 90°
a ) 20.34440(10) Å
b ) 21.5072(4) Å
c ) 44.4859(6) Å
R ) 90°
a ) 14.34090(1) Å
b ) 18.0504(3) Å
c ) 20.9629(3) Å
R ) 113.7360(10)°
â ) 91.0210(10)°
γ ) 90.8190°
4965.26(11) Å3, 4
1.366 mg/cm3
3.680 mm-1
2052
a ) 15.2784(4) Å
b ) 16.9614(4) Å
c ) 22.1374(6) Å
R ) 90°
â ) 115.326°
γ ) 90°
â ) 90°
γ ) 90°
â ) 104.7243(8)°
γ ) 90°
volume, Z
8539.5(11) Å3, 8
1.450 mg/cm3
4.190 mm-1
3808
19464.9(5) Å3, 16
1.407 mg/cm3
3.728 mm-1
8400
5548.4(2) Å3, 4
1.374 mg/cm3
3.241 mm-1
density (calculated)
absorption coefficient
F(000)
2324
crystal size
θ range
limiting indices
0.18 × 0.22 × 0.44 mm
0.12 × 0.19 × 0.42 mm
0.14 × 0.24 × 0.30 mm
0.34 × 0.20 × 0.20 mm
2.80-26°
2.20-29.32°
2.12-29.04°
1.38-31.97°
-52 e h e 47, -1 e k e 14, -27 e h e 27, -29 e k e 24, -18 e h e 15, -24 e k e 23, -22 e h e 14, -25 e k e 24,
-1 e l e 23
10081
8354 [R(int) ) 0.0607]
XABS2
-60 e l e 52
174787
46937 [R(int) ) 0.0838]
SADABS
-27 e l e 27
41206
22349 [R(int) ) 0.1189]
SADABS
-31 e l e 30
48663
17097 [R(int) ) 0.0648]
SADABS
reflections collected
independent reflections
absorption correction
max. and min.
1.256 and 0.787
0.831 and 0.597
0.831 and 0.417
0.928 and 0.629
transmission
refinement method
full-matrix least-squares
full-matrix-block least-squares full-matrix least-squares
full-matrix least-squares
on F2
17095/0/555
on F2
8340/0/400
0.873
on F2
on F2
data/restraints/param
46747/13/1742
1.136
22349/60/885
0.921
goodness-of-fit on F2
0.948
final R indices [I > 2σ(I)] R1 ) 0.0369, wR2 ) 0.0768 R1 ) 0.0653, wR2 ) 0.1131
R indices (all data) R1 ) 0.0661, wR2 ) 0.0816 R1 ) 0.0934, wR2 ) 0.1250
largest diff peak and hole 1.684 and -1.392 eA-3 2.254 and -1.115 eA-3
R1 ) 0.0729, wR2 ) 0.1627
R1 ) 0.1102, wR2 ) 0.1737
5.920 and -2.937 eÅ-3
R1 ) 0.0518, wR2 ) 0.1099
R1 ) 0.0748, wR2 ) 0.1239
2.978 and -4.336 eA-3
and rel intensity) ν(CdO) 1605 (s) (12C material); Elemental Analysis
for C31H71GeN3O3P2PtSi4 unobtainable, product rapidly loses CO2.
(Et3P)2PtN(Ph)C(O)N(Ph)OGe[N(SiMe3)2]2 (9a). 3a (50 mg, 0.06
mmol) was dissolved in 0.25 mL of C6H6. PhNCO (5 µL, 0.06 mmol)
was added to the unstirred solution. After 40 min crystals began to
form. The crystals were collected by reduced pressure filtration under
nitrogen to yield 33 mg of 9 (59% isolated yield). 1H NMR (CDCl3)
δ 0.16 (br, 36H, Si(CH3)3), 0.98 (m, 9H, CH2CH3), 1.14 (m, 9H,
CH2CH3), 1.48 (m, 3H, CH2CH3), 1.87 (m, 3H, CH2CH3), 2.05 (m,
3H, CH2CH3), 2.29 (m, 3H, CH2CH3), 6.60 (t, aromatic), 6.84 (t, 1H,
aromatic), 6.97 (t, 1H aromatic), 7.13 (t, 2H, aromatic), 7.15 (d, 2H,
aromatic), 7.38 (t, 2H, aromatic), 7.88 (t, 2H, aromatic); 13C NMR
C30H71GeN3OP2PtSi4 (3a). An orange crystalline plate of dimen-
sions 0.18 × 0.22 × 0.44 mm was mounted and placed in a cold stream
of nitrogen at 178(2) K. Additional details: Scan method ω, scan rate
variable 2-5°/min, background-to-scan ratio 0.5, ω scan range 5-52°
(h: -52/47; k: 0/14; l: 0/23), 10 081 measured, merged to 8354 unique
reflections, Rint ) 0.0607 empirical absorption correction.
C33H70GeN3O3P2PtSSi4 (6a‚3C6H6). A small, colorless rectangular
crystal (dimensions ) 0.12 × 0.19 × 0.42 mm) was mounted and
placed in a cold nitrogen stream at 158(2) K; the detector was placed
at a distance of 4.577 cm from the crystal. The integration of the data
using a primitive orthorhombic unit cell yielded a total of 174 787
reflections to a maximum of 2θ value of 58.64° of which 46 937 were
independent and 36 887 were greater than 2σ(I). The final cell constants
were based on the xyz centroids of 8192 reflection above 10σ(I).
Analysis of the data showed negligible decay during data collection.
Transmission coefficients ranged from 0.597 to 0.831. The structure
was solved in the space group Pna21 with Z ) 16 for the formula
C33H70GeN3O3P2SSi4Pt. The final full matrix refinement based on F2
converged at R1 ) 0.0934 and wR2 ) 0.1250 (based on all data); the
largest peak in the final difference map was 2.254 Å and was associated
with the Pt.
C34H76GeN3O2P2PtSi4 (7a‚C6H6). A colorless rectangular block
having dimensions 0.14 × 0.24 × 0.30 mm was mounted and placed
in a cold nitrogen stream at 158(2) K; the detector was placed at a
distance of 5.057 cm from the crystal. The integration of the data using
a triclinic cell yielded a total of 90 474 reflections to a maximum 2θ
value of 59.8° of which 44 710 were independent and 13 435 were
greater than 2σ(I). The final cell constants were based on the xyz
centroids of 7856 reflection above 10σ(I). Analysis of the data showed
negligible decay during data collection. Transmission coefficients
ranged from 0.417 to 0.831. The structure was solved in the space
group P1h with Z ) 4 for the formula C34H76GeN3O2P2PtSi4. The final
full matrix refinement based on F2 converged with R1 ) 0.0729 and
wR2 ) 0.1627 (based on observed data); R1 ) 0.1102 and wR2 )
0.1737 (based on all data); the largest peak in the final difference map
was 5.9 Å and was associated with Pt.
3
(CDCl3) δ 166.6 (d, JP-C ) 2.4 Hz, CdO), 151.9 (s, quaternary
aromatic), 145.4 (s, quaternary aromatic), 128.5 (s, aromatic), 127.5
(s, aromatic), 127.2 (s, aromatic), 123.4 (s, aromatic), 122.0 (s,
aromatic), 119.0 (s, aromatic), 20.0 (m, CH2CH3), 16.1 (m, CH2CH3),
9.62 (m, CH2CH3), 8.24 (s, Si(CH3)3), 7.94 (s, Si(CH3)3), 7.59(s, Si-
(CH3)3), 7.34 (s, Si(CH3)3); 31P{1H} NMR (CDCl3) δ 6.1 (d w/ 195Pt
1
2
satellites, JPt-P ) 3377 Hz, JP-P ) 19.0 Hz), -14.2 (d w/195Pt
satellites, 1JPt-P ) 1851 Hz, 2JP-P 19.0 Hz); IR (KBr) 1616 (vs) cm-1
,
ν(CdO); Elemental Analysis Calcd for C37H76GeN4O2P2PtSi4: C, 42.28;
H, 7.29; N, 5.33. Analysis C, 41.79; H, 6.79; N, 5.07.
X-ray Crystal Structure Determinations. Crystals were mounted
on a glass fiber with paratone N hydrocarbon oil. X-ray data for 6a,
7a, and 9a were collected on a Siemens SMART diffractometer with
a CCD area detector equipped with a normal focus Mo-target X-ray
tube (λ ) 0.71073 A) operated at 2000 W power (50 kV, 40 mA). A
total of 2132 frames were collected with a scan width of 0.3° in ω and
an exposure time of 30 s/frame. The frames were integrated with
Siemens’ SAINT software package with a narrow frame algorithm. The
structures were solved and refined with the Siemens SHELXTL (version
5.03) software package. The data were corrected for absorption using
an empirical method (SADABS). X-ray data for 3a was collected on
a Siemens R3/v automated diffractometer with graphite monochroma-
tized Mo KR radiation (λ ) 0.71073 Å) and solved by using direct
methods with the program SHELXTL PLUS. All non-hydrogen atoms
were allowed to refine anisotropically, with hydrogen atoms placed in
idealized positions. Table 1 provides a general summary of crystal-
lographic parameters. Specific data for each structure follows.
C46H85GeN4O2P2PtSi4 (9a‚1.5C6H6). A small, colorless rectangular
blocklike crystal (dimensions ) 0.34 × 0.20 × 0.20) was mounted
and placed in a cold stream of nitrogen on the diffractometer at 153(2)

Arylnitroso Substrates on a Platinum-Germylene Complex
J. Am. Chem. Soc., Vol. 120, No. 30, 1998 7487
K; the detector was placed at a distance of 4.577 cm from the crystal.
Integration of the data using a primitive monoclinic unit cell yielded a
total of 48 663 reflections to a maximum of 2θ value of 64° of which
17 097 were independent and 12 687 were greater than 2σ(I). The final
cell constants (Table 1, XYZ) were based on the xyz centroids of 8192
reflection above 10σ(I). Analysis of the data showed negligible decay
during data collection. Transmission coefficients ranged from 0.629
to 0.928. The structure was solved in the space group P2(1)/c with Z
) 4 for the formula C46H85N4O2P2Si4GePt. The final full matrix
refinement based on F2 converged at R1 ) 0.0748 and wR2 ) 0.1239
(based on all data); the largest peak in the final difference map was
2.97 Å and was associated with the Pt.
Variable Temperature (VT) NMR Spectra of 3b. VT-NMR
spectra of 3b were recorded in toluene-d8 on a Varian AMX-400
spectrometer at 399.967 MHz. Temperatures were measured by means
of a thermocouple mounted in the spectrometer probe and calibrated
to accuracy within (0.1 °C. At each temperature increment, the
instrument was reshimmed after the sample had equilibrated for 10
min. Line shape analysis of the obtained data was determined by
manual measurements of the fwhm with caliper calibrated to +0.001
mm. The obtained spectra and tabulated rate measurements are included
in the Supporting Information.
Attempted Reaction of 2,4,6-Tri-tert-butylnitrosobenzene with
1. A flame sealed NMR tube was charged with 12 mg (0.015 mmol)
of 1 co-mixed with 4 mg (0.015 mmol) of 2,4,6-tri-tert-butylnitrosoben-
zene dissolved in 0.25 mL of C6D6. No immediate reaction was
observed. The sample was then heated in an oil bath to 80 °C for 2 h.
Analysis of the tube by NMR spectroscopy showed no reaction as
evidenced by the presence of only starting materials.
Attempted Reaction of N-Nitrosodimethylamine with 1. In the
same manner as above, 35 mg (0.042 mmol) of 1 was allowed to react
with 3 µL (0.041 mmol) of N-nitrosodimethylamine. At 20 °C, the
NMR spectrum showed no reaction as evidence by presence of
unreacted starting material. Heating the tube to 80 °C for 2 h also
failed to induce reaction.
Variable temperature NMR studies were used to explore the
origin of the broad trimethlysilyl peak observed for 3b.10
Cooling a toluene-d8 solution to -55 °C resulted in four sharp,
distinct -SiMe3 resonances. These peaks broadened as the
solution was warmed, coalescing to a single, very broad feature
at 25 °C. Upon heating the solution, two peaks began to grow
out of the broad feature, resulting in two fairly sharp peaks at
60 °C. Continued heating to 105 °C resulted in a second
coalesence to a single broad feature. Two separate dynamic
events were determined to be present via line shape analysis of
spectra collected between -55 and 105 °C. In the low-
temperature region, the barrier was calculated to be 50 ( 2 kJ/
mol. The barrier was observed to be associated with a
conversion from two to four -SiMe3 peaks and has been
interpreted as the barrier to rotation of the Ge-N bond in this
sterically hindered molecule. In the high-temperature region,
the barrier was calculated to be 116 ( 1 kJ/mol and was
assigned as the barrier to nitrogen inversion. The typical range
of nitrogen inversion barriers previously observed is 175-313
kJ/mol,11 considerably greater in energy than the barrier
observed in this system. Although the role M-N bonding plays
in the energy of nitrogen inversion is not well understood, the
low barrier observed is consistent with the trend toward planar
nitrogen typically observed for this class of complexes (Vida
infra). This assignment is further supported by the observation
of both R and S isomeric products in the crystallographic
analysis of 3a (Vida infra). Attempts to observe the nitrogen
inversion barrier in 3a by NMR spectroscopy were unsuccessful,
although some broadening of the -SiMe3 peak was observed
upon cooling to -90 °C. The dramatic difference in dynamic
behavior between 3a and 3b is most likely related to the position
of the 2-methyl group in 3b which places it in direct steric
conflict with the -SiMe3 groups.
To assess the extent of activation of the nitroso group, and
unambiguously assign the connectivity, single-crystal X-ray
analysis of 3a was obtained (Figure 1). As judged from the
N-O bond distance of 1.498(6) Å, the nitrosobenzene is highly
activated. This extremely long N-O bond is obtained in a
system known to reversibly form metallacycles under very mild
conditions.3 It is interesting to note that this high degree of
N-O activation, as judged by the N-O bond length, does not
require highly oxophilic, irreversible reactions. The four-
membered metallacycle displays noticeable distortion from
planarity as evidenced by the 16° dihedral angle between the
Pt-Ge and N-O bond vectors. Coordination about germanium
resembles a distorted trigonal pyramid: the base formed by
platinum and the nitrogen atoms bound to germanium and the
cap formed by the oxygen of nitrosobenzene. Direct compari-
sons to a (µ-η2-nitrosobenzene-N)(µ-η1,η1-nitrosobenzene-N,O)-
(η1-nitrosobenzene-N)tris(trimethylphosphine)diplatinum(II) (4)
Attempted Reaction of Dimethylacetylenedicarboxylate (DMAD)
with 3a. DMAD (1 equiv) was allowed to react with 50 mg (0.06
mmol) of 3a dissolved in 0.25 mL of C6D6. The NMR tube was fitted
with a rubber septum and protected from light with aluminum foil. No
reaction was observed over a period of 72 h at 20 °C as evidenced by
1
the presence of unreacted starting material in the H NMR spectrum.
Results and Discussion
Reaction of Nitrosobenzene and 2-Nitrosotoluene with
(Et3P)2PtGe[N(SiMe3)2]2. Nitrosobenzene (1 equiv) underwent
rapid reaction at -50 °C with a toluene solution of 1 causing
a color change from golden yellow to deep orange. After
removal of volatiles, recrystallization from hexane gave an
orange powder, (Et3P)2PtN(Ph)OGe[N(SiMe3)2]2 (3a). 2-Ni-
trosotoluene reacts under the same conditions to form the
analogous orange product, (Et3P)2PtN(o-Tol)OGe[N(SiMe3)2]2
(3b). Characterization of 3a by 1H, 13C, and 31P NMR
spectroscopy indicated the presence of two inequivalent trieth-
ylphosphine ligands, suggesting the adoption of a square-planar
geometry about the platinum as well as a single phenyl group
1
and equivalent trimethylsilyl groups. The H NMR spectrum
of 3b gave an analogous set of spectral features, but the
resonance for the trimethylsilyl groups was very broad at 20
°C, suggesting a dynamic process on the NMR time scale. IR
spectra revealed the absence of a NdO stretching mode for both
complexes. In analogy to previously observed results for the
reaction of carbon dioxide with 1,3 we assigned the structure
as a four-membered metallacycle with N bound to Pt and O
bound to Ge as indicated in eq 1. The decision regarding the
orientation of the nitrosobenzene binding was based primarily
upon steric considerations, as the opposite orientation would
place the phenyl group in conflict with the bulky bis(trimeth-
ylsilyl)amide groups.
(10) VT-NMR spectra are provided in the Supporting Information.
(11) For leading references into energetic issues in nitrogen inversion
barriers, see: (a) Lehn, J. M. Fortschr. Chem. Forsch. 1970, 15, 311. (b)
Nelsen, S. F.; Ippoliti, J. T.; Frigo, T. B.; Petillo, P. A. J. Am. Chem. Soc.
1989, 111, 1776. (c) Belostotskii, A. M.; Gottlieb, H. E.; Hassner, A. J.
Am. Chem. Soc. 1996, 118, 7783.

7488 J. Am. Chem. Soc., Vol. 120, No. 30, 1998
Litz et al.
Figure 3. Histogram of N-O bond lengths having the connectivity
shown in inset.
(5) of 1.410(7) Å, is significantly shorter than found in 3a.
Figure 3 shows a histogram of N-O bond lengths compiled
from a search of the Cambridge Structural Database (CSD) for
N-bound metal complexes.13 Examination of the resulting
histogram reveals that most N-O bonds having this connectivity
lie within 1.315 and 1.470 Å (91%). Only the N-O bond of
3a exceeds 1.480 Å. The degree of pyramidalization observed
for the nitrogen center is also quite rare. A search of the CSD
for all M-N(R)O- derivatives finds that of the 89 complexes
crystallographically characterized to date, the sum of the three
nitrogen angles is generally between 352 and 364° (85 ex-
amples). Four complexes, all ArNO molecules side-bound to
a metal center via the NO moeity so as to form a three-
membered ring, have a three angle sum between 288 and
296°.6a,14 For these molecules, the very acute M-N-O angle
internal to the three-membered ring provides one angle between
60 and 70°. The other two angles are approximately 109°. The
three angle sum for complex 3a is 348°, making it one of only
five such complexes characterized to data with a three angle
sum less than 352°. 3a can be described as a metallaoxaziridine,
although all previous such complexes have contained ArNO
side-bound to a single metal center. The pyramidizalization of
the nitrogen atom in 3a is probably related to the geometrical
constraints imposed by the four-membered ring. Note that the
similar µ-η2-nitrosobenzene binding mode observed for 4,
forming a five-membered ring, gives an almost perfectly planar
nitrogen atom with a three angle sum of 359.4°.12
Geoffroy et al. postulated that the reaction of (CO)5WdCR2
with PhNO forms a four-membered metallocycle intermediate
on route to the observed ketone product and proposed metal-
nitrene (Figure 4, pathway A).15 Products were also observed
supporting the presence of pathway B. To the best of our
knowledge, 3a represents the first isolated and characterized
analogue of the proposed metallocycle intermediate. In contrast
to the result for (CO)5WdCR2, 1 forms only one of the two
possible metallacycles. The extremely long N-O bond suggests
the metathesis observed for the carbene system may be poised
to occur in the germylene system, and indeed, 3a is both
thermally and photochemically sensitive.16 Unfortunately, ef-
forts to trap potential metal nitrene and germanone species with
dimethyl acetylenedicarboxylate, 2,3-dimethylbutadiene, and
methyl-tert-butyl ketone were unsuccessful, and no products
Figure 1. ORTEP of 3a (50% probability). Bond lengths (Å) and
angles (deg): Pt1-Ge1, 2.4214(7); Pt1-N3, 2.088(5); Pt1-P1, 2.249-
(2); Pt1-P2, 2.356(2); N3-O1, 1.498(6); Ge1-O1, 1.820(4); Ge1-
N2, 1.877(4); Ge1-N1, 1.884(4); C25-N3, 1.381(7); O1-Ge1-Pt1,
84.55(13); N3-Pt1-Ge1, 66.00(13); N3-Pt1-P2, 97.32(13); P1-
Pt1-P2, 96.08(6); O1-N3-Pt1, 106.1(3); N3-O1-Ge1, 95.8(3); N1-
Ge1-N2, 113.8(2) P1-Pt1-Ge1, 99.76(5); C25-N3-Pt1, 131.7(4);
C25-N3-O1, 109.8(4); N1-Ge1-Pt1, 122.49(14); N2-Ge1-Pt1,
120.16(14); N1-Ge1-O1, 104.7(2); N2-Ge1-O1, 100.2(2).
Figure 2. Trogler et al. (µ-η2-nitrosobenzene-N)(µ-η1,η1-nitrosoben-
zene-N,O)(η1-nitrosobenzene-N)tris(trimethylphosphine)diplatinum-
(II) (5).
complex synthesized by Trogler et al. containing three ni-
trosobenzene binding modes is instructive (Figure 2).12
4
contains one µ-η2-nitrosobenzene with an N-O bond distance
of 1.433(15) Å that bridges both Pt atoms in a binding mode
similar to that observed for 3a. The Pt-N interaction of 1.976-
(11) Å is somewhat shorter than the 2.088(5) Å observed for
3a. The Pt-O distance of 2.043(8) Å in 4 is somewhat larger
than the 1.95 Å predicted by covalent radii; however, the Ge-O
distance observed in 3a, 1.820(4) Å, is slightly shorter than the
1.88 Å predicted by covalent radii. The weaker binding of the
nitrosobenzene oxygen by Pt may be the key factor in the shorter
N-O bond observed for the binding mode in 4. Even the µ-η1-
nitrosobenzene of 4, depicted as a formal zwitterion by Trogler
et al., which has an N-O bond distance of 1.428(27) Å, is 0.070
Å shorter than 3a. Prior to the synthesis of 3a, 4 was noted to
possess the longest N-O bond of any metal-nitroso complex.12
Based on this comparison, one might have expected the charge
distribution in 3a to make the nitrogen atom quite electrophilic.
However, the insertion chemistry we have observed is consistent
with a nucleophilic character generally observed for metal-bound
nitroso compounds. The N-O bond length in a more standard
square-planar Pt nitroso complex such as (Ph3P)2Pt(η2-ONPh)
(13) 3D search using the Cambridge Structural Database; Allen, F. H.;
Kennard, O. Chemical Design Automated News 1993, 8, 31.
(14) (a) Liebeskind, L. S.; Sharpless, K. B.; Wilson, R. D.; Ibers, J. A.
J. Am. Chem. Soc. 1978, 100, 7061. (b) Brouwer, E. B.; Legzdins, P.; Rettig,
S. J.; Ross, K. J. Organometallics 1994, 13, 2088. (c) Ridouane, F.; Sanchez,
J.; Arzoumanian, H.; Pierrot, M. Acta Crystallogr. C 1990, 46, 1407.
(15) Pilato, R. S.; Williams, G. D.; Geoffroy, G. L.; Rheingold, A. L.
Inorg. Chem. 1988, 27, 3665-3668.
(12) Packet, D. L.; Trogler, W. C.; Rheingold, A. L. Inorg. Chem. 1987,
26, 4309.
(16) The more sterically crowded 3b has considerably more thermal
stability. It does not begin to decompose until ∼105 °C.

Arylnitroso Substrates on a Platinum-Germylene Complex
J. Am. Chem. Soc., Vol. 120, No. 30, 1998 7489
Scheme 1. Insertion Reactions of 3a and 3b with SO2,
H2CO, CO2, and PhNCO
Figure 4. Proposed metathesis mechanism for the reaction of arylni-
trosocomplexes with metal carbenes.
could be isolated or identified. Related attempts to isolate the
nickel analogues of 3a and 3b using (Ph3P)2NiGe[N(SiMe3)2]2
(2) were unsuccessful, resulting in complex mixtures found to
contain ∼4% of bis(triethylphosphine)azobenzene nickel (II),
by comparison of NMR shifts to a known standard.17 This
product may result from a metathesis reaction similar to that
proposed by Geoffroy but could also result from known oxygen
atom transfer reactions that occur in Ni(0)/nitrosobenzene
mixtures.18 Attempts to synthesize other analogues of 3a and
3b were made. However, both 2,4,6-tri-tert-butylnitrosobenzene
and N-nitrosodimethylamine failed to react with 1, even when
heated to 80 °C.
Insertion Reactions. A significant literature describing the
coordination and reaction chemistry of C-nitroso-compounds
exists.19 An interesting and well studied class of reactions
involves insertion into the Pt-N bond, primarily investigated
for (Ph3P)2Pt(η2-ONPh) 5; where the behavior was attributed
to nucleophilic attack by the nitroso-N.6 Reagents observed to
insert into 5 include PhNCO, CO2, CS2, benzylidenmalononi-
trile, tetracyanoethylene, benzaldehyde, and dimethylacetylene
dicarboxylate. Since the binding modes of nitrosobenzene in
3a and 5 were quite different, we pursued a series of insertion
reactions to explore this class of reactivity in our system.
Scheme 1 illustrates the chemical reactivity observed for 3a
with SO2, H2CO, PhNCO, and CO2 and 3b with SO2 and H2-
CO. Some general observations about each of the resulting
heterocycles are informative. First, only dipolar substrates were
observed to insert into the Pt-N bond to give ring expansion.
As previously noted,6 the most electropositive atom of the
substrate’s site of unsaturation undergoes nucleophilic attack
by the nitroso nitrogen. Second, no evidence of attack at the
Pt-Ge bond has been observed. Third, both five- and six-
membered rings have been generated. The rings exhibit
dynamic behavior at 20 °C in solution. The insertion reactions
of SO2 and H2CO have not previously been observed for other
M-nitroso complexes. In contrast to the behavior of the three-
membered heterocycle 5, no reaction was observed for 3a or
3b with dimethylacetylene dicarboxylate, acetaldehyde, or
benzaldehyde.
quite soluble in chloroform and THF. Characterization by 1H,
13C, and 31P NMR spectroscopy indicated the presence of two
inequivalent triethylphosphine ligands, suggesting the adoption
of a square-planar geometry about the platinum as well as a
single phenyl group. A broad single peak was observed for
the -SiMe3 groups, suggesting the presence of dynamic
processes such as those discussed for 3b. The IR spectrum
revealed the presence of stretching modes attributable to an SO2
functionality at 1384 and 1165 cm-1
. Elemental analysis
confirmed the uptake of 1 equiv of SO2. We originally believed
that three structures for 6a were possible: (1) SO2 directly
adding across the weakened N-O bond, (2) SO2 directly adding
across the Pt-Ge bond, or (3) SO2 inserting into the Pt-N bond.
The third structure was initially ruled out due to the lack of
literature precedence for such reactions occurring with M-ni-
troso compounds. Results with CO2 and other reagents gave
us confidence that the Pt-Ge bond was not the site of insertion.
Therefore we initially assigned the structure as SO2 insertion
across the weakened N-O bond in analogy to Cowie’s proposal
that SO2 reacted with an elongated O-O bond in a four-
membered metallacycle to generate a bridging sulfate com-
plex.20,21 Likewise, SO2 was observed to reversibly insert into
the N-N bond of [Fe2(CO)6(µ-N2Ph2)].22
To unambiguously determine the site and orientation of SO2
incorporation, single-crystal X-ray analysis of 6a was obtained
(Figure 5). Surprisingly, SO2 was found to insert into the Pt-N
bond. The four independent molecules, possessing the con-
nectivity portrayed in Scheme 1, were observed to have similar
bond lengths, yet there existed two pairs of molecules varying
significantly in terms of the N-O-Ge bond angle (101.4(5)°
vs 108.1(5)°), inversion at nitrogen, and therefore ring confor-
Reaction of SO2 with 3a and 3b. SO2 (1 equiv) reacts
readily with a stirred -78 °C toluene solution of 3a resulting
in an immediate color change from orange to light yellow. After
removal of volatiles, the contents of the flask were extracted
with a minimum of THF. Dropwise addition of an equal volume
of Et2O gave large colorless crystals over 24 h. The crystals
displayed limited solubility in benzene and toluene yet were
(20) (a) Vaartstra, B. A.; Xiao, J.; Cowie, M. A. J. Am. Chem. Soc. 1990,
112, 9425-9426. (b) Xiao, J.; Santarsiero, B. D.; Vaartstra, B. A.; Cowie,
M. A. J. Am. Chem. Soc. 1993, 115, 3212.
(21) Additional examples of SO2 insertions into platinum-bound perox-
ides: (a) Horn, R. W.; Weissberger, E.; Collman, J. P. Inorg. Chem. 1970,
9, 2367. (b) Valentine, J.; Valentine, D.; Collman, J. P. Inorg. Chem. 1971,
10, 219. (c) Cook. C. D.; Jauhal, G. S. J. Am. Chem. Soc. 1967, 89, 3066.
(d) Farrar, D. H.; Gukathasan, R. R. J. Chem. Soc., Dalton Trans. 1989,
557. (e) Bhaduri, S.; Johnson, B. F.; Khair, A.; Ghatak, I.; Mingos, D. M.
P. J. Chem. Soc., Dalton Trans. 1980, 1572.
(17) Ittel, S. D. Inorg. Synth. 1990, 28, 98-104.
(18) (a) Otsuka, S.; Aotani, Y.; Tatsuno, Y.; Yoshida, T. Inorg. Chem.
1976, 15, 656-660. (b) Berman, R. S.; Kochi, J. K. Inorg. Chem. 1980,
19, 248-254.
(19) For a review, see: Cameron, M.; Gowenlock, B. G.; Vasapollo, G.
Chem. Soc. ReV. 1990, 19, 355-379.
(22) Kabir, S. E.; Ruf, M.; Vahrenkamp H. J. Organomet. Chem. 1996,
512, 261-263.

7490 J. Am. Chem. Soc., Vol. 120, No. 30, 1998
Litz et al.
Figure 5. ORTEP of (S)-6a (50% probability). Bond lengths (Å) and
angles (deg): Pt1-Ge1, 2.4715(11); Pt1-P1, 2.373(3); Pt1-P2, 2.307-
(3); Pt1-S1, 2.319(3); Ge1-N2, 1.889(8); O3-N1, 1.424(10); Ge1-
O3, 1.861(7); Ge1-N3, 1.873(9); S1-O1, 1.478(8); S1-O2, 1.477(7);
S1-N1, 1.778(8); N1-C13, 1.453(12); S1-Pt1-P1, 89.78(9); P2-
Pt1-P1, 96.06(10); S1-Pt1-Ge1, 82.25(7); O1-S1-O2, 113.0(4);
P1-Pt1-Ge1, 170.72(8); N1-S1-Pt1, 104.2(3); N3-Ge1-N2, 113.7-
(4); N1-O3-Ge1, 101.4(5); O3-Ge1-Pt1, 98.2(2); O3-N1-S1,
106.6(5); O1-S1-Pt1, 114.0(3); O2-S1-Pt1, 114.5(3); O1-S1-N1,
107.8(4); O2-S1-N1, 102.0(4); S1-N1-C13, 115.1(6); O3-N1-
C13, 110.3(7); N2-Ge1-O3, 99.0(3); N3-Ge1-O3, 99.7(3); N2-
Ge1-Pt1, 116.1(3); N3-Ge1-Pt1, 123.0(3).
Figure 6. ORTEP of (R)-7a (50% probability). Bond lengths (Å) and
angles (deg): Pt1-Ge1, 2.4874(9); Pt1-P1, 2.291(3); Ge1-O2, 1.909-
(6); C13-N1, 1.500(12); Ge1-N2, 1.929(7); Pt1-O1, 2.106(7); Pt1-
P2, 2.384(2); O2-N1, 1.476(9); O1-C13, 1.425(11); Ge1-N3,
1.952(8); N1-C14, 1.470(12); O1-Pt1-Ge1, 77.0(2); Pt1-O1-C13,
120.9(5); O1-C13-N1, 114.2(7); C13-N1-O2, 108.3(6); N1-O2-
Ge1, 113.0(4); O2-Ge1-Pt1, 102.9(2); P1-Pt1-P2, 102.40(9); Ge1-
Pt1-P1, 101.25(7); C14-N1-O2, 109.4(7); N2-Ge1-N3, 106.5(3);
O1-Pt1-P2, 79.2(2); C14-N1-C13, 111.4(8); N2-Ge1-Pt1, 115.9-
(2); N3-Ge1-Pt1, 127.6(2); N2-Ge1-O2, 98.9(3); N3-Ge1-O2,
99.4(3).
mation. The average N-O bond distance of 1.43 (1) Å is still
quite long. The average N-S bond length of 1.78 (1) Å is
longer than 98% of the previously characterized N-S bonds
according to the Cambridge crystallographic database.13 Plati-
num’s coordination sphere resembles a distorted square plane
comprised of cis-ligated triethylphosphines and a bidentate
sulfoximido-germyl moiety.
of any simple, homogeneous, structurally characterized ana-
logues of the key Contact Process intermediates, the isolation
of 6a represents an interesting, although crude first model. The
closest analogues previously structurally characterized were
peroxodisulfate ions.23 Unfortunately, we have been unable to
observe interconversion of 6a to an imido analogue of the
metal-sulfate complex.
The observation of SO2 insertion into the Pt-N bond, as
opposed to insertion into the N-O bond, provides the first
isolated and characterized example of a metal-bound -S(O)2N-
(R)O- moiety, a species closely related to an elusive key
intermediate proposed in the platinum-catalyzed Contact Process
for the oxidation of SO2 (eq 2).7 Previous oxygen labeling
experiments suggested that such insertion pathways should be
considered because of the distribution of label in the final sulfate
product. Collman et al. proposed intermediate species that did
not contain a direct M-S bond such as B for the iridium
complex used in their study, although species A could also
account for the isotopic distribution observed.21a,b
Reaction of H2CO with 3a and 3b. Paraformaldehyde was
allowed to react with a stirring benzene solution of 3a. Reaction
progress was monitored visually by disappearance of the initial
orange color. The product was isolated by filtration from excess
paraformaldehyde and was recrystallized from pentane as an
off-white powdery solid. IR spectroscopy revealed the absence
1
of a CdO stretch, and H and 13C NMR data indicated that a
single formaldehyde molecule had been complexed. Cis-
inequivalent triethylphosphine ligands, a single phenyl ring, an
upfield shifted methylene carbon, and no observable Pt-C
coupling led us to assign the structure indicated in Scheme 1
for 7a. Note that this is also consistent with the general
observation that the nitroso-N acts as a nucleophile in the
insertion reaction. Reaction of paraformaldehyde with 3b gave
the analogue 7b.
X-ray crystallographic analysis of 7a confirmed our structural
assignment (Figure 6). Two independent molecules were
observed in the crystal lattice. The dissymmetric isomers are
nonsuperimposable mirror images differing by a ring flip with
inversion at the ring nitrogen. The overall structure can best
be described as a six-membered heterometallacycle possessing
a cyclohexane-like boat conformation. The boat conformation
avoids the 1,3-diaxial strain that would exist between the phenyl
ring and the bulky -N(SiMe3)2 moiety of germanium in the
chair conformation. 7a is noteworthy as it is the first well
characterized example of an aldehyde inserting into a metal-
C-nitroso-compound leading to an O-bound hydroxamate-like
moiety.
To the best of our knowledge, no complexes have been
isolated and structurally characterized to date containing the
connectivity of elements outlined in intermediates A or B;
however, 6a is an isoelectronic analogue of intermediate A,
albeit bridging over two metal centers. Given the apparent lack

Arylnitroso Substrates on a Platinum-Germylene Complex
J. Am. Chem. Soc., Vol. 120, No. 30, 1998 7491
Reaction of CO2 with 3a. A 10-fold excess of 10% 13CO2/
CO2 was condensed into an NMR-tube containing a d6-benzene
solution of 3a. The tube was flame sealed, and upon thawing
rapid clarification of the initially orange solution was observed.
1H, 13C, and 31P NMR spectroscopy indicated quantitative
conversion to a new complex which possessed cis-inequivalent
triethylphosphine ligands, a new set of phenyl resonances, and
an upfield shifted trimethylsilyl singlet. The IR and 13C NMR
spectra revealed a carbamate-like CdO was present at 1605
cm-1 and 161.5 ppm, respectively. As in the cases of 7a and
7b, no 195Pt satellites were observable, suggesting the absence
of a direct Pt-C bond. To examine this phenomenon, we
synthesized and structurally characterized a complex containing
2
a bridging carbonate adduct which should possess a JPt-C
,
(Et3P)2Pt(O13C(O)O)Ge[N(SiMe3)2]2 (10), to serve as a model
for 2JPt-C constants in these systems.24 The 13C NMR spectrum
of concentrated samples of 10 were unable to detect the presence
of two-bond 195Pt satellites. Given this close comparison, the
absence of 195Pt satellites in 8a is not surprising. Attempts to
isolate and structurally characterize 8a were thwarted due to
the rapid loss of CO2 during workup, indicating reversible
complexation. Based upon the spectroscopic evidence, and the
chemical analogies presented in this paper, we assign the product
of this reaction as shown in Scheme 1 for 8a.
Figure 7. ORTEP of 9a (50% probability). Bond lengths (Å) and
angles (deg): Pt1-Ge1, 2.4562(5); Ge1-O1, 1.867(3); Ge1-N4,
1.883(3); Ge1-N3, 1.904(4); Pt1-N1, 2.112(3); Pt1-P1, 2.2692(11);
Pt1-P2, 2.3776(12); N1-C1, 1.368(5); N1-C2, 1.411(5); N2-C1,
1.394(5); N2-O1, 1.405(4); N2-C13, 1.433(5); C1-O2, 1.237(5);
N4-Ge1-N3, 105.6(2); O1-Ge1-Pt1, 99.44(9); P1-Pt1-P2, 94.48-
(4); N1-Pt1-Ge1, 76.47(10); C1-N2-O1, 119.2(3); N2-O1-Ge1,
120.5(2); N1-Pt1-P2, 89.42(10); P1-Pt1-Ge1, 101.57(3); C1-N1-
Pt1, 117.9(3); N1-C1-N2, 113.9(4); N4-Ge1-Pt1, 121.99(11); N3-
Ge1-Pt1, 126.78(11); N3-Ge1-O1, 97.69(14); N4-Ge1-O1, 96.00-
(14); Pt1-N1-C2, 119.1(3); C2-N1-C1, 119.7(3); N1-C1-O2,
126.0(4); O2-C1-N2, 120.0(4); C1-N2-C13, 122.2(3); C13-N2-
O1, 111.1(3).
Reaction of PhNCO with 3a. To an unstirred benzene
solution of 3a, 1 equiv of PhNCO was added by syringe. After
40 min, the clarified solution began to form colorless crystals.
The long, thin hexagonal plates were collected by filtration,
washed with benzene, and dried in vacuo. Characterization by
IR spectroscopy revealed urea-like CdO stretching frequencies
at 1616 and 1588 cm-1 1H, 13C, and 31P NMR spectroscopy
.
gave evidence of cis-inequivalent triethylphosphines ligated to
platinum, two inequivalent phenyl rings, and an intact germylene
moiety. Given the presence of the intact CdO, we assigned
the structure as shown in Scheme 1 for 9a which resembles an
N-bound urea fragment spanning the Pt-Ge-O fragment. To
unambiguously assign the connectivity as well as to confirm
the presence an intact Pt-Ge bond, analysis by single-crystal
X-ray diffraction was obtained. An ORTEP diagram of 9a is
shown in Figure 7 with key bond lengths and angles. The six-
membered heterometallacycle displays considerable distortion
from planarity analogous to the boat conformer of cyclohexane
rings. This conformation allows the phenyl rings to occupy a
trans-configuration with respect to the Pt-Ge vector and
minimizes 1,3 diaxial steric interaction with neighboring
N(SiMe3)2 groups. Ligand coordination about platinum re-
sembles a distorted square-planar environment. The Pt-N bond
length of 2.112(3) Å is somewhat longer than the 2.088(5) Å
observed for 3a. Both N(1) and N(2) are planar as expected
for nitrogen atoms bound to a carbonyl moiety.
membered ring of 3a contains a Pt-Ge-O angle of 84.55(13)°,
thus considerable p-character is likely involved in ring-bonding,
increasing the s-character in the Ge-N bonds. Insertion of SO2
into 3a, gives a five-membered ring complex 6a in which this
angle remains the same at 113.7(4)°. However, insertion of
H2CdO or PhNCO to form six-membered rings 7a and 9a gives
bond angles of 106.5(3)° and 105.6(2)°, respectively. This
observation is consistent with an increase in the Pt-Ge-O bond
angle to 102.9(2)° for 7a and 99.44(9)° for 9a. Other related
structures published to date include a complex with no
constraining ring, (Et3P)2Pt(H)GeH[N(SiMe3)2]2. In this in-
stance a N-Ge-N angle of 106.9(4)° is observed.3 Another
species that contains a four-membered ring, (Et3P)2PtC(O)OGe-
[N(SiMe3)2]2, exhibits a N-Ge-N bond angle of 110.0(3)°.
Based on the trends discussed, the Pt-Ge-O angle for this
complex would be expected to be between 85 and 105°.
However, the experimentally determined value is 81.7(2)°,3 even
more acute than that observed for 3a. Thus, although the bond
angles can be rationalized for many of the structures as changes
in the amount of p-character at Ge, this simple explanation does
not suffice for all cases characterized to date. None of the other
metrical parameters such as Pt-Ge or Ge-O bond distance
correlate with the variation in N-Ge-N angle. The four-
coordinate germyls present in all of these complexes adopt a
roughly trigonal pyramidal geometry.
The variation of the N-Ge-N bond angle in all of these
structures is curious. In general, germylenes have Q-Ge-Q
bond angles substantially less than the nominal 120° because
of the large amount of s-character in the lone-pair and large
amount of p-character in the ligand bonds.25 Consistent with
maintaining a germylene character, the N-Ge-N bond angle
of 1 is 106.3(3)°.3 Upon complexation of the nitrosobenzene
to form 3a, this angle opens up to 113.8(2)°. The four-
Conclusions
Arylnitroso compounds bind to group-10 metal-germylene
complexes accompanied by an extremely lengthened N-O bond
(23) a) Harrison, W. D.; Hathaway, B. J. Acta Crystallogr. B 1980, 36,
1069. (b) Blackman, A. G.; Huffman, J. C.; Lobkovsky, E. B.; Christou,
G. J. Chem. Soc. Chem. Commun. 1991, 989.
(25) (a) Fjeldberg, T.; Haaland, A.; Schilling, B. E. R.; Lappert, M. F.;
Thorne, A. J. J. Chem. Soc., Dalton Trans. 1986, 1551. (b) Grev, R. S.;
Schaefer, H. F. Organometallics 1992, 11, 3489.
(24) Litz, K. E.; Banaszak Holl, M. M. Unpublished results.

7492 J. Am. Chem. Soc., Vol. 120, No. 30, 1998
Litz et al.
of 1.498(6) Å; currently the longest N-O bond of any
M-nitroso complex. Chemical implications of the binding were
explored using a series of Pt-N insertion reactions with SO2,
CO2, H2CO, and PhNCO which formed new S-N or C-N
bonds. Despite the extremely lengthened N-O bond, the
activations of dipolar substrates occurred only at the Pt-N bond
and avoided cleavage of the N-O and Pt-Ge bonds. Thermal
and photochemical reactions appearing to cleave the N-O bond
resulted in a myriad of products. Insertion of SO2 into the Pt-N
bond of 3a was particularly interesting because the platinum
germylene provided the stabilization necessary to allow isolation
and structural characterization of a model for a key step in SO2
oxidation. Overall, these reactions highlight the ability of the
Pt-Ge nexus to activate organic substrates to further modifica-
tion. Contrary to the common situation observed for small
molecule activations occurring at metal-metal bonds, the Pt-
Ge interaction is robust and remains intact. Sufficient electrons
are present in the Ge(II) ligand to promote continued ligation
to the platinum as a germyl fragment. We are pursuing
chemistry designed to eliminate the nascent, novel heterocycles
and regenerate (Et3P)2PtGe[N(SiMe3)2]2 (1).
Acknowledgment. Alfa-Aesar is thanked for a loan of K2-
PtCl4. M.M.B.H. thanks the University of Michigan for support
of this work and D. Coucouvanis, M. D. Curtis, A. J. Ashe,
and an anonymous reviewer for helpful discussions and
constructive criticism.
Supporting Information Available: Tables of crystal data,
atomic coordinates, bond lengths and angles, anisotropic
displacement parameters, and hydrogen coordinates and isotropic
displacement parameters, VT-NMR spectrum, and N-inversion
rates and rate of Ge-N rotation for 3b (54 pages, print/PDF).
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instructions.
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