Atom transfer reactions of (TTP)Ti(n2-3-hexyne): Synthesis and molecular structure of trans-(TTP)Ti[OP(Oct)3]2

Article abstract of DOI:10.1021/ic0003426

Atom and group transfer reactions were found to occur between heterocumulenes and (TTP)Ti(n²-3-hexyne), 1 (TTP = meso-5,10,15,20-tetra-p-toly]porphyrinato dianion). The imido derivatives (TTP)Ti=NR (R = ′Pr, 2; ′Bu, 3) were produced upon treatment of complex 1 with ′PrN=C=N′Pr, ′PrNCO, or ′BuNCO. Reactions between complex 1 and CS₂, ′BuNCS, or ′BuNCSe afforded the chalcogenido complexes, (TTP)Ti=Ch (Ch = Se, 4; S, 5). Treatment of complex 1 with 2 equiv of PEt₃ yielded the bis(phosphine) complex, (TTP)Ti(PEt₃)₂, 6. Although (TTP)Ti(n²-3-hexyne) readily abstracts oxygen from epoxides and sulfoxides, the reaction between 1 and O=P(Oct)₃ did not result in oxygen atom transfer. Instead, the paramagnetic titanium(II) derivative (TTP)-Ti[O=P(Oct)₃]₂, 7, was formed. The molecular structure of complex 7 was determined by single-crystal X-ray diffraction: Ti-O distance 2.080(2) A and Ti-O-P angle of 138.43(10)°. Estimates of Ti=O, Ti=S, Ti=Se, and Ti=NR bond strengths are discussed.

Full text of DOI:10.1021/ic0003426

Inorg. Chem. 2001, 40, 499-506
499
Atom Transfer Reactions of (TTP)Ti(η2-3-hexyne): Synthesis and Molecular Structure of
trans-(TTP)Ti[OP(Oct)3]2
Joseph L. Thorman,† Victor G. Young, Jr.,‡ Peter D. W. Boyd,§ Ilia A. Guzei,† and
L. Keith Woo*,†
Department of Chemistry, Iowa State University, Ames, Iowa 50011-3111, Department of Chemistry,
University of Minnesota, Minneapolis, Minnesota 55455, and Department of Chemistry, University of
Auckland, Private Bag 92019, Auckland, New Zealand
ReceiVed March 30, 2000
Atom and group transfer reactions were found to occur between heterocumulenes and (TTP)Ti(η2-3-hexyne), 1
i
(TTP ) meso-5,10,15,20-tetra-p-tolylporphyrinato dianion). The imido derivatives (TTP)TidNR (R ) Pr, 2;
tBu, 3) were produced upon treatment of complex 1 with iPrNdCdNiPr, iPrNCO, or tBuNCO. Reactions between
t
t
complex 1 and CS2, BuNCS, or BuNCSe afforded the chalcogenido complexes, (TTP)TidCh (Ch ) Se, 4;
S, 5). Treatment of complex 1 with 2 equiv of PEt3 yielded the bis(phosphine) complex, (TTP)Ti(PEt3)2, 6.
Although (TTP)Ti(η2-3-hexyne) readily abstracts oxygen from epoxides and sulfoxides, the reaction between 1
and OdP(Oct)3 did not result in oxygen atom transfer. Instead, the paramagnetic titanium(II) derivative (TTP)-
Ti[OdP(Oct)3]2, 7, was formed. The molecular structure of complex 7 was determined by single-crystal X-ray
diffraction: Ti-O distance 2.080(2) Å and Ti-O-P angle of 138.43(10)°. Estimates of TidO, TidS, TidSe,
and TidNR bond strengths are discussed.
toluene, and hexane were freshly distilled from purple solutions of
sodium benzophenone and brought into the glovebox without exposure
Introduction
New insight concerning atom transfer reactions have emerged
in the past few years. However, relatively few systematic studies
involving transfer of multivalent atoms or groups to transition
metal compounds have been conducted due to the lack of
suitable, well-behaved low-valent metal acceptor complexes. An
exemplary case was reported by Mayer involving oxidative
addition and group transfer reactions with WCl2(PMePh2)4.1
From this study the WdO bond strength was estimated to be
g138 kcal/mol. Similarly, rhenium-oxygen bond strengths have
also been addressed.2 In related group 4 transition metal
complexes the large free energy barrier to oxygen atom
abstraction from titanium(IV) oxo complexes is well-known.3
Consequently, Ti2+ is an effective reducing agent and should
be a potent atom transfer acceptor. This was recently demon-
strated in a previous study of Ti(II), where (TTP)Ti(η2-3-
hexyne), 1, was able to abstract oxygen and sulfur from a
number of substrates.4 This reactivity is unique and has not been
documented for other divalent titanium compounds under
ambient conditions.5 In this report, further chemistry of Ti(II)
is described. With new atom transfer reactions, estimates for
the TidX multiple bond strengths are derived.
to air. (TTP)Ti(η2-3-hexyne)4c and tBuNCSe6 were prepared according
to published procedures. Compounds tBuNCO and tBuNCS were
purchased from Aldrich, vacuum-distilled, and dried by passage through
a column of activated, neutral alumina. CS2 was purchased from Fisher
Scientific, vacuum-distilled, and dried over molecular sieves. The
magnetization of 2 was measured at a field of 3 T over the range 6-296
K on a Quantum Design MPMS SQUID magnetometer. Corrections
for the diamagnetic molar susceptibility were implemented for the
porphyrin (-731 × 10-6 cgs/mol)7 and OdP(Oct)3 (-302.7 × 10-6
cgs/mol).8 1H NMR data were recorded on either a Varian VXR (300
(4) Woo, L. K.; Hays, J. A.; Young, V. G., Jr.; Day, C. L.; Caron, C.;
D′Souza, F.; Kadish, K. M. Inorg. Chem. 1993, 32, 4186. (b) Wang,
X.; Woo, L. K. J. Org. Chem. 1998, 63, 356. (c) Wang, X.; Gray, S.
D.; Chen, J.; Woo, L. K. Inorg. Chem. 1998, 37, 5.
(5) Peulecke, N.; Baumann, W.; Kempe, R.; Burlakov, V. V.; Rosenthal,
U. Eur. J. Inorg. Chem. 1998, 419. (b) Varga, V.; Mach, K.; Polasek,
M.; Sedmera, P.; Hiller, J.; Thewalt, U.; Troyanov, S. I. J. Organomet.
Chem. 1996, 506, 241. (c) Hill, J. E.; Profilet, R. D.; Fanwick, P. E.;
Rothwell, I. P. Angew. Chem., Int. Ed. Engl. 1990, 29, 664. (d) Fochi,
G.; Florine, C.; Bart, J. C. J.; Giuunchi, J. J. Chem. Soc., Dalton Trans.
1983, 1515. (e) Stahl, L.; Ernst, R. D. J. Am. Chem. Soc. 1987, 109,
5673. (f) Stahl, L.; Trakarnpruk, W.; Freeman, J. W.; Arif, A. M.;
Ernst, R. D. Inorg. Chem. 1995, 34, 1810. (g) McPherson, A. M.;
Fieselmann, B. F.; Lichtenberger, D. L. McPherson, G. L.; Stucky,
G. D. J. Am. Chem. Soc. 1979, 101, 3425. (h) Cohen, S. A.; Auburn,;
P. R.; Bercaw, J. E. J. Am. Chem. Soc. 1983, 105, 1136. (i) Fachinetti,
G.; Floriani, C. J. J. Chem. Soc., Chem. Commun. 1974, 66. (j)
Fachinetti, G.; Floriani, C. J. Chem. Soc., Dalton Trans. 1974, 2433.
(k) Fachinetti, G.; Floriani, C.; Stoeckli-Evans, H. J. Chem. Soc.,
Dalton Trans. 1977, 2297. (l) Fachinetti, G.; Biran, C.; Floriani, C.;
Chiesi Villa, A.; Guastini, C. J. Chem. Soc., Dalton Trans. 1979, 792.
(m) Bottomley, F.; Chin, T. T.; Egharevba, G. O.; Kane, L. M.; Pataki,
D. A.; White, P. S. Organometallics 1988, 7, 1214. (n) Girolami, G.
S.; Wilkinson, G.; Galas, A. M. R.; Thornton-Pett, M.; Hursthouse,
M. B. J. Chem. Soc., Dalton Trans. 1985, 1339.
Experimental Section
General Procedures. All manipulations were performed under an
inert atmosphere of nitrogen using a Vacuum Atmospheres glovebox
equipped with a Model MO-40M Dri-Train gas purifier. Benzene-d6,
* To whom correspondence should be addressed.
† Iowa State University.
‡ University of Minnesota, X-ray Crystallographic Laboratory.
§ University of Auckland.
(1) Bryan, J. C.; Mayer, J. M. J. Am. Chem. Soc. 1990, 112, 2298.
(2) Conry, R. R.; Mayer, J. M. Inorg. Chem. 1990, 29, 4862. (b) Gable,
K. P.; Juliette, J. J. J.; Li, C.; Nolan, S. P. Organometallics 1996, 15,
5250.
(6) Sonoda, N.; Yamamot, G.; Tsutsum, S. Bull. Chem. Soc. Jpn. 1972,
45, 2937.
(7) Sutter, T. P. G.; Hambright, P.; Thorpe, A. N.; Quoc, N. Inorg. Chim.
Acta 1992, 195, 131.
(3) Holm, R. H. Chem. ReV. 1987, 87, 1401.
(8) Lister, M. W.; Marson, R. Can. J. Chem. 1964, 42, 1817.
10.1021/ic0003426 CCC: $20.00 © 2001 American Chemical Society
Published on Web 12/28/2000

500 Inorganic Chemistry, Vol. 40, No. 3, 2001
Thorman et al.
MHz, 20 °C) or Bruker DRX (400 MHz, 25 °C) spectrometer. Chemical
shifts were referenced to proton solvent impurities (δ 7.15 ppm, C6D5H).
UV-vis data were recorded on a HP8452A diode array spectropho-
tometer and reported as λmax in nm (log ꢀ). Elemental analyses were
performed by Iowa State University Instrument Services. Although
hotter, longer combustion conditions were used, carbon analysis was
often low. For metalloporphyrin complexes, this is likely due to the
formation of metal carbides during combustion.9
and C6D6 (≈0.6 mL). Within 5 min all the 3-hexyne had been displaced
and a small amount of (TTP)TidO was present. Allowing the solution
1
to stand at 25 °C for 96 h produced (TTP)TidO in 43% yield. H
NMR (C6D6, 300 MHz): (TTP)TidO,11 9.24 (s, 12H, â-pyrrole), 8.00
(d, 8H, meso-C6H4CH3), 7.28 (d, 8H, meso-C6H4CH3), 2.42 (s, 12H,
meso-C6H4CH3).
Reaction of 1 with tBuNCSe. An NMR tube equipped with a Teflon
stopcock was charged with 1 (12.27 mg, 15.36 µmol), Ph3CH (95.0
(TTP)TidNiPr, 2. Method A: Isopropylisocyanate (44 µL, 0.448
mmol) was added to a stirred solution of 1 (304 mg, 0.380 mmol) in
toluene (≈10 mL). After 1 h at ambient temperature the dark blue
solution was filtered and the filtrate reduced to dryness in vacuo.
Recrystallization at -25 °C for 1 day from a toluene solution (8 mL)
layered with heptane (4 mL) afforded analytically pure product (128
mg, 44% yield). UV/vis (toluene): 549 (4.53), 424 (5.57), 399
(shoulder, 4.70). 1H NMR (C6D6, 400 MHz): 9.24 (s, 12H, â-pyrrole),
8.27 (d, 4H, meso-C6H4CH3), 8.05 (d, 4H, meso-C6H4CH3), 7.31 (t,
8H, meso-C6H4CH3), 2.42 (s, 12H, meso-C6H4CH3), -0.45 (m, 1H,
-NCHMe2), -1.66 (d, 6H, -NCHMe2). Anal. Calcd. for C51H43N5Ti:
C, 79.16; H, 5.60; N, 9.05. Found: C, 78.72; H, 5.67; N, 8.73. Method
B: An NMR tube equipped with a Teflon stopcock was charged with
complex 1 (14.3 mg, 17.8 µmol), Ph3CH (89.5 µL of 0.1455 M in
C6D6, 13.0 µmol), iPrNdCdNiPr (3.2 µL, 20.4 µmol), and C6D6 (≈0.6
mL). The solution immediately darkened and the imido complex (TTP)-
TidNiPr (14.2 µmol, 79% yield) had formed over 12 h at ambient
µL, 0.146 M, 13.82 µmol), BuNCSe (5.4 mg, 33.3 µmol), and C6D6
t
(≈0.6 mL). The solution was allowed to stand at 25 °C for 4 h at which
t
time BuNC (14.73 µmol) and (TTP)TidSe (15.20 µmol, 99% yield)
were observed. Further monitoring of the sample revealed that after
all the (TTP)TidSe was formed, (TTP)Ti(η2-Se2) was being produced
t
1
by the reaction between (TTP)TidSe and excess BuNCSe. H NMR
(C6D6, 300 MHz): (TTP)TidSe,4a 9.31 (s, 8H, â-H), 8.18 (d, 4H, meso-
C6H4CH3), 7.95 (d, 4H, meso-C6H4CH3), 7.28 (m, 8H, meso-C6H4CH3),
t
2.41 (s, 12H, meso-C6H4CH3); BuNC, 0.86 (s, 9H); (TTP)Ti(η2-Se2),
9.08 (s, 8H, â-H), 8.15 (d, 4H, meso-C6H4CH3), 7.89 (d, 4H, meso-
C6H4CH3), 7.26 (m, 8H, meso-C6H4CH3), 2.39 (s, 12H, meso-C6H4CH3).
At early times an intermediate was observed. 1H NMR (C6D6, 300 MHz)
[(TTP)Ti(η2-tBuNCSe)]: 9.01 (s, 8H, â-H), 8.43 (d, 4H, meso-C6H4-
CH3), 7.96 (d, 4H, meso-C6H4CH3), 7.29 (dd, 8H, meso-C6H4CH3), 2.39
(s, 12H, meso-C6H4CH3), -0.52 (s, 9H, η2-tBuNCSe).
Reaction of 1 with Cy3PdS. An NMR tube equipped with a Teflon
stopcock was charged with 1 (8.9 mg, 11.12 µmol), Ph3CH (92.5 µL,
0.146 M, 13.46 µmol), Cy3PdS (4.0 mg, 12.8 µmol), and C6D6 (≈0.6
mL). After ≈5 min (TTP)TidS (1.47 µmol, 13% yield) and 1 (6.96
1
i
temperature. H NMR (C6D6, 300 MHz): PrNC, 2.84 (spt, 1H), 0.65
(d, 6H). The 1H NMR spectrum of (TTP)TidNiPr was experimentally
identical to that reported in Method A.
1
µmol) were present. H NMR (C6D6, 300 MHz): (TTP)TidS,4a 9.29
i
Reaction of Complex 1 with PrNCO. An NMR tube equipped
(s, 12H, â-pyrrole), 8.14 (d, 4H, meso-C6H4CH3), 7.95 (d, 4H, meso-
C6H4CH3), 7.30 (m, 8H, meso-C6H4CH3), 2.41 (s, 12H, meso-C6H4CH3).
(TTP)Ti(PEt3)2, 6. A stirred solution of complex 1 (230 mg, 0.287
mmol) in toluene (≈10 mL) was treated with PEt3 (120 µL, 0.812
mmol). After being stirred for 1.5 h at ambient temperature, the solution
was filtered and the filtrate reduced to dryness in vacuo. The residue
was recystallized from a toluene/hexanes (2:1) solution that was allowed
to stand at -25 °C for 1 day, which produced analytically pure black
crystals of complex 6 in two crops (145 mg, 53% yield). UV/vis
(toluene): 553(4.45), 426 (5.53), 406 (shoulder, 2.61). 1H NMR (C6D6,
400 MHz): 11.50 (bd, 12H, J ) 7 Hz, P(CH2CH3)3, 7.22 (bs, 18H,
P(CH2CH3)3), 6.14 (d, 8H, J ) 8 Hz, meso-C6H4CH3), 4.82 (d, 8H, J
) 8 Hz, meso-C6H4CH3), 1.47 (s, 12H, meso-C6H4CH3), -5.92 (bs,
8H, â-pyrrole). Anal. Calcd. for C60H66N4P2Ti: C, 75.62; H, 6.98; N,
5.88. Found: C, 75.75; H, 7.35; N, 5.80.
(TTP)Ti[(OP(Oct)3)]2, 7. A round-bottom flask was charged with
complex 1 (364 mg, 0.455 mmol) and OdP(Oct)3 (362 mg, 0.935
mmol). Upon addition of toluene (≈15 mL), the stirred solution became
dark blue. The solution was concentrated in vacuo after 2.5 h to a black
oil (≈1 mL). This oil was redissolved in hexanes (≈24 mL) and then
reduced in vacuo to 4 mL and cooled to -25 °C for 1 day, which
produced analytically pure black crystals of complex 7 (355 mg, 52%
yield). UV/vis (hexane): 550 (2.14), 422 (5.69), 403 (shoulder, 2.98).
1H NMR (C6D6, 300 MHz): 12.11 (bs, 12H, 2-CH2), 10.27 (bs, 12H,
3-CH2), 8.72 (d, 8H, meso-C6H4CH3), 4.65 (bs, 12H, 4-CH2), 4.55 (s,
12H, meso-C6H4CH3), 3.03 (bs, 12H, 5-CH2), 2.02 (bs, 12H, 6-CH2),
1.33 (bs, 12H, 7-CH2), 1.18 (bs, 18H, 8-CH3), -0.43 (d, 8H, meso-
C6H4CH3), -33.0 (bs, 8H, â-pyrrole). 31P NMR (C6D6, 81 MHz): 83.5
ppm, referenced to internal H3PO4 (0.00 ppm). (Free OdP(Oct)3, -31.8
ppm) Anal. Calcd. for C96H138N4O2P2Ti: C, 77.39; H, 9.34; N, 3.76.
Found: C, 76.89; H, 9.06; N, 3.08.
with a Teflon stopcock was charged with complex 1 (13.1 mg, 16.4
µmol), Ph3CH (92.0 µL, 0.146 M, 13.4 µmol), iPrNCO (2.60 µL, 26.5
µmol), and C6D6 (≈0.6 mL). Within 5 min (TTP)TidNiPr (16.6 µmol,
1
100% yield) was produced. The H NMR spectrum of (TTP)TidNiPr
was experimentally identical to that reported in Method A.
t
Reaction of Complex 1 with BuNCO. An NMR tube equipped
with a Teflon stopcock was charged with complex 1 (5.93 mg, 7.43
µmol), Ph3CH (84.0 µL, 0.181 M, 15.2 µmol), tBuNCO (1.2 µL, 10.5
µmol), and C6D6 (≈0.6 mL). Within 5 min (TTP)TidNtBu was
produced in 48% yield. Allowing the solution to stand at 25 °C for 16
h produced (TTP)TidNtBu (7.39 µmol, 99% yield) as the only
1
observable diamagnetic porphyrin species. The H NMR is identical
to the literature spectrum for (TTP)TidNtBu:10 9.24 (s, 12H, â-pyrrole),
8.32 (d, 4H, meso-C6H4CH3), 8.04 (d, 4H, meso-C6H4CH3), 7.34 (d,
4H, meso-C6H4CH3), 7.30 (d, 4H, meso-C6H4CH3), 2.42 (s, 12H, meso-
C6H4CH3), -1.58 (s, 9H, -NtBu). CO was detected in a separate
experiment with a Kratos MS50TC mass spectrometer. Calcd.: 27.99491
m/z. Found: 27.99491 ( 0.0028 m/z.
Reaction of 1 with tBuNCS. An NMR tube equipped with a Teflon
stopcock was charged with 1 (10.65 mg, 13.33 µmol), Ph3CH (92.5
µL, 0.1455 M, 13.46 µmol), tBuNCS (2.8 µL, 22.07 µmol), and C6D6
(≈0.6 mL). When the solution was allowed to stand at 25 °C for 13 h,
1
(TTP)TidS (12.94 µmol, 97% yield) was produced. H NMR (C6D6,
300 MHz): CNtBu, 0.86 (s, 9H); (TTP)TidS,4a 9.29 (s, 12H, â-pyrrole),
8.14 (d, 4H, meso-C6H4CH3), 7.95 (d, 4H, meso-C6H4CH3), 7.30 (m,
8H, meso-C6H4CH3), 2.41 (s, 12H, meso-C6H4CH3).
Reaction of Complex 1 with CS2. An NMR tube equipped with a
Teflon stopcock was charged with complex 1 (12.2 mg, 15.3 µmol),
Ph3CH (85.0 µL, 0.181 M, 15.4 µmol), CS2 (1.2 µL, 20.0 µmol), and
C6D6 (≈0.6 mL). Heating the solution at 80 °C for 112 h produced
(TTP)TidS (12.5 µmol, 82% yield). 1H NMR (C6D6, 300 MHz) (TTP)-
TidS:4a 9.29 (s, 8H, â-H), 8.14 (d, 4H, meso-C6H4CH3), 7.95 (d, 4H,
meso-C6H4CH3), 7.30 (m, 8H, meso-C6H4CH3), 2.41 (s, 12H, meso-
C6H4CH3).
Structure Determination of (TTP)Ti(PEt3)2, 6 and (TTP)Ti[OP-
(Oct)3]2, 7. Crystallographic data for complexes 6 and 7 are found in
Table 1. A crystal of complex 7 was attached to a glass fiber and
mounted on a Siemens SMART system for data collection at 173(2)
K. Final cell constants were calculated from a set of 8192 strong
reflections from the actual data collection. The space group P21/n was
Reaction of Complex 1 with (MeO)2SO. An NMR tube equipped
with a Teflon stopcock was charged with complex 1 (6.3 mg, 7.7 µmol),
Ph3CH (90.5 µL, 0.145 M, 13.1 µmol), (MeO)2SO (1.7 µL, 20.0 µmol),
determined from systematic absences and intensity statistics.12
A
(9) Ikeda, O.; Fukuda, H.; Tamura, H. J. Chem. Soc., Faraday Trans. 1
1986, 82, 1561-1573.
(10) Gray, S. D.; Thorman, J. L.; Berreau, L. M.; Woo, L. K. Inorg. Chem.
1997, 36, 278.
(11) Fournari, C.; Guilard, R.; Fontesse, M.; Latour, J.-M.; Marchon, J.-
C. J. Organomet. Chem. 1976, 110, 205.
(12) SHELXTL-Plus V5.0; Siemens Industrial Automation, Inc.: Madison,
WI, 1998.

Synthesis and Structure of trans-(TTP)Ti[OP(Oct)3]2
Inorganic Chemistry, Vol. 40, No. 3, 2001 501
Table 1. Crystal Data and Structure Refinement for Compounds
(TTP)Ti(PEt3)2, 6, and (TTP)Ti[OP(Oct)3]2, 7
optimization was carried out for the [Ti(porphine)(OP(CH3)3)2] complex
in the spin singlet state. A spin unrestricted open-shell calculation was
carried out for this molecule in a triplet state using the singlet-state
optimized geometry.
compound
empirical formula
fw
(TTP)Ti(PEt3)2 (TTP)Ti[OP(Oct)3]2
C60H66N4P2Ti
953.01
173(2) K
0.71073 Å
P1h
C96H138N4O2P2Ti
1489.94
173(2) K
0.71073 Å
P21/n
Results
temp
wavelength
space group
a, Å
b, Å
c, Å
i
t
Reactivity of (TTP)Ti(η2-3-hexyne) with PrNCO, BuN-
CO, and PrNdCdNiPr. Quantitative nitrene group transfer,
i
10.9163(6)
11.5404(6)
20.7951(11)
83.747(1)
78.928(1)
85.252(1)
2550.5(2)
2
10.2196(1)
28.6024(5)
15.4589(2)
90
96.169(1)
90
as monitored by 1H NMR spectroscopy, resulted from treatment
of (TTP)Ti(η2-3-hexyne), 1, with PrNCO or BuNCO. Within
i
t
R, deg
5 min complete displacement of 3-hexyne and a 50% production
â, deg
i
t
of the imido complex (TTP)TidNR (R ) Pr, 2, Bu, 3) was
observed. After 16 h, quantitative formation of the imido
complex occurred (eq 1).
γ, deg
vol, Å3
4492.55(11)
2
Z
density (calcd)
absorption coeff
1.241 Mg/m3
0.274 mm-1
1.101 Mg/m3
0.179 mm-1
R1 ) 0.0548,
wR2 ) 0.1138
final R indices [I > 2σ(I)]a R1 ) 0.1262,
wR2 ) 0.3514
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo )2]]0.5
.
2
The formation of CO was confirmed by high-resolution mass
spectrometry (found: 27.99491 ( 0.0028 m/z; calcd.: 27.99491).
Over the course of these reactions, intermediate substitution
products were not observed. Because of mechanical losses,
complex 2 was isolated in 44% yield. The isopropyl imido
complex 2 could also be prepared by treatment of 1 with 1,3-
diisopropylcarbodiimide, although mass balance was not realized
during spectroscopic monitoring. In this case the yield of the
imido complex (TTP)TidNiPr, 2, was only 79% as measured
by H NMR. The isocyanide side product, PrNC, can also
displace the alkyne from (TTP)Ti(η2-3-hexyne) to form a
paramagnetic, 1H NMR silent bis(isocyanide) complex, (TTP)-
Ti(iPrNC)2. However, treatment of the sample with excess
pyridine in an attempt to convert any NMR silent porphyrin
species to the NMR active complex (TTP)Ti(py)2 did not reveal
additional Ti complexes.
Despite the reduced steric bulk of the isopropyl group, the
imido complex is quite air- and water-stable in comparison to
previous titanium metalloporphyrin derivatives. For example,
(TTP)TidNtBu, 3, was hydrolyzed within minutes upon expo-
sure to moisture to form free amine and (TTP)TidO. In contrast,
the isopropyl complex, 2, required hours to undergo complete
hydrolysis.
successful direct-methods solution was calculated, which provided most
non-hydrogen atoms from the E-map. Several full-matrix least-squares/
difference Fourier cycles were performed, which located the remainder
of the non-hydrogen atoms. All non-hydrogen atoms were refined with
anisotropic displacement parameters. All hydrogen atoms were placed
in ideal positions and refined as riding atoms with relative isotropic
displacement parameters. Complex 6 was treated in an analogous
manner. A crystal of complex 6 was attached to a glass fiber and
mounted on a Bruker CCD-1000 diffractometer for data collection at
173(2) K. A total of 28 087 data was harvested by collecting four sets
of frames with 0.3° scans in ω with an exposure time of 90 s per frame.
These highly redundant data sets were corrected for Lorentz and
polarization effects. The absorption correction was based on fitting a
function to the empirical transmission surface as sampled by multiple
equivalent measurements.13 Final cell constants were calculated from
a set of 6649 strong reflections from the actual data collection. The
space group P1h was determined from systematic absences and intensity
statistics.14 A successful direct-methods solution was calculated, which
provided most non-hydrogen atoms from the E-map. Several full-matrix
least squares/difference Fourier cycles were performed, which located
the remainder of the non-hydrogen atoms. Because of poor quality of
the diffraction data, all atoms were refined with isotropic displacement
coefficients. All hydrogen atoms were included in the structure factor
calculation at idealized positions and were allowed to ride on the
neighboring atoms with relative isotropic displacement coefficients.
There are two symmetry-independent half molecules of complex 6 in
the asymmetric unit. These half molecules occupy crystallographic
inversion centers. The X-ray analysis of complex 6 confirmed atom
connectivity, but did not provide reliable metrical parameters. Thus,
bond distances and angles for compound 6 are not reported.
1
i
Reactivity of (TTP)Ti(η2-3-hexyne) with tBuNCSe, tBuNCS,
and CS2. Quantitative displacement of the 3-hexyne was
observed by 1H NMR within minutes upon addition of tBuNCSe
to (TTP)Ti(η2-3-hexyne). In addition to the appearance of the
terminal selenido complex, (TTP)TidSe, 4, an additional set
of sharp porphyrin signals was detected at early times (eq 2).
Computational Details. Density functional calculations were per-
formed using the Amsterdam Density Functional program.15 Double-ú
Slater-type basis sets were used for C(2s, 2p), N(2s, 2p), O(2s, 2p),
P(3s, 3p), and H(1s) augmented by a single 3d polarization function.
A triple-ú basis set was used for Ti(3s, 3p, 3d, 4s). The inner electron
configurations were assigned to the core and were treated using the
frozen core approximation. All calculations were carried out using the
local density approximation due to Vosko, Wilk, and Nusair16 with
nonlocal corrections for exchange due to Becke17 with nonlocal
corrections for correlation due to Lee, Yang, and Parr.18 A full geometry
The ratio of complex 4 to the new intermediate was 1:9 after
≈5 min. Associated with this new transient complex was a
9-proton singlet at -0.52 ppm. This signal is downfield from
the tBu resonance of the imido species, (TTP)TidNtBu, by over
1 ppm. An η2-C,Se bound isoselenocyanate, (TTP)Ti(η2-tBu-
NCSe), is a reasonable formulation for this intermediate. At 20
°C the intermediate is slowly converted over 4 h to complex 4
(99% NMR yield) and tBuNC. Treatment of the hexyne complex
(13) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(14) All software and sources of the scattering factors are contained in the
SHELXTL V5.1 program library, G. Sheldrick, Bruker Analytical
X-ray Systems, Madison, WI.
(15) (a) ADF 2.3.0, Theoretical Chemistry, Vrije Universiteit, Amsterdam.
(b) Baerends, E. J.; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2, 41. (c)
te Velde, G.; Baerends, E. J. J. Comput. Phys. 1992, 99, 84.
(16) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200.
(17) Becke, A. D. Phys. ReV. A 1988, 38, 3098.
(18) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785.

502 Inorganic Chemistry, Vol. 40, No. 3, 2001
Thorman et al.
1 with tBuNCS proceeded somewhat faster to form the terminal
chalcogenido (TTP)TidS (95% NMR yield after ≈15 min). An
additional set of broad, transient NMR signals (∆ν1/2 ) 16 Hz)
was detected, which had experimentally similar chemical shifts
to those for (TTP)Ti(η2-tBuNCSe). This species is therefore
assigned as an η2-C,S adduct, (TTP)Ti(η2-tBuNCS).
Table 2. Selected Intramolecular Bond (Å) Distances and Angles
(deg) of Complex 7
Ti-O
2.080(2)
1.513(2)
2.064(2)
2.071(2)
2.064(2)
2.071(2)
Ti-O-P
O-Ti-N2
O-Ti-N1
138.43(10)
95.95(7)
89.39(7)
O-P
Ti-N1
Ti-N2
Ti-N1
Ti-N2
Heating a benzene-d6 solution of 1 in the presence of ≈1.25
equiv of CS2 at 80 °C for 112 h produced (TTP)TidS, 5, in
87% yield by NMR. This reaction proceeded with the formation
of at least five intermediate titanium porphyrin species, indicated
2. The titanium resides in an octahedral coordination environ-
ment with the pyrrole nitrogens in the equatorial plane and the
OP(Oct)3 ligands occupying the axial positions (Figure 1). A
1
by the number of â-pyrrole signals in the H NMR spectrum.
Synthesis of (TTP)Ti(PEt3)2, 6. Although no reaction was
observed between (TTP)Ti(η2-3-hexyne) and NEt3, N(Oct)3, or
P(Oct)3, treatment with PEt3 rapidly afforded the bis(phosphine)
adduct (TTP)Ti(PEt3)2, 6, in 53% isolated yield (eq 3). This
reaction is quantitative by NMR. Although 6 is paramagnetic,
1
its H NMR signals are relatively sharp and integrations are
sufficient for determining the metal:ligand stoichiometry. This
situation is common for S ) 1 Ti(II) complexes.4c For example,
the â-pyrrole resonance at -5.92 ppm integrated as eight protons
relative to the 18-H methyl signals for the two PEt3 ligands at
7.22 ppm. The coordination environment of titanium was found
to contain trans-PEt3 groups by X-ray diffraction, despite poorly
diffracting crystals.19 Phosphorus signals for the PEt3 groups
were not observed in the 31P NMR spectrum.
Synthesis and Structure of (TTP)Ti[(OPOct3)]2, 7. Tri-
octylphosphine oxide readily displaced 3-hexyne from complex
1 within 5 min to produce the bis(phosphine oxide) adduct,
(TTP)Ti[OP(Oct)3]2, 7 (eq 4). The significant solubility of this
Figure 1. Thermal ellipsoid representation of (TTP)Ti[OP(Oct)3]2.
Thermal ellipsoids drawn at the 50% probability level. Tolyl groups
have been omitted.
number of Ti(IV) complexes containing O-bound phosphine
oxide ligands have been crystallographically characterized,20 but
there appears to be only one Ti(II) compound containing Ti-O
bonds. The Ti-O bond distances in complex 7 (2.080(2) Å)
are significantly longer than the Ti-O single-bond distances
observed for Ti(OPh)2(1,2-bis(dimethylphosphino)ethane)2 (1.891-
(6), 1.930(6) Å).21 The tetravalent imido complex, TiCl2(dNtBu)-
(OPPh3)2, possesses Ti-O bonds of 2.008(6) and 2.047(6) Å
and Ti-O-P angles of 159.2(4)° and 154.6(4)°.20a The Ti-
O-P angle of 138.43(10)° in complex 7 is surprisingly acute
in light of the potential steric interaction between the octyl
groups and the porphyrin macrocycle. This appears to be the
most acute M-O-P bond angle observed for a monodentate
phosphine oxide-transition metal complex.22,23 Although crys-
tallographically characterized transition metal phosphine oxide
analogues are known in a variety of oxidations states and
coordination environments, no clear trend exists with M-O-P
bond angles.23 The Ti-O vector in complex 7 is canted with
respect to the normal of the N4 plane by 6°, resulting in a Ti-P
distance of 3.365 Å. This is well outside of an η2-bonding
interaction.24,25 The O-P bond distance in 7 (1.513(2) Å) is
comparable to those of free phosphine oxides (1.490-1.498
Å).26 The OP(Oct)3 moiety in 7 is perhaps best described by
compound in hexane prevented isolated yields higher than 52%.
However, this reaction proceeded nearly quantitatively (93%)
in an NMR tube experiment with an internal standard. Assign-
ment of this complex as a bis(phosphine oxide) adduct was
1
facilitated by H NMR spectroscopy. The â-carbon methylene
resonance (12.11 ppm) integrated as 12 protons for two OP-
(Oct)3 groups relative to the 12 proton methyl resonance (4.55
ppm) of the porphyrin tolyl groups. The 31P chemical shift for
complex 7 was significantly deshielded relative to that of free
OPOct3. Similar behavior has been observed in other phosphine
oxide adducts, although to a lesser extent.20
(21) Morris, R. J.; Girolami, G. S. Inorg. Chem. 1990, 29, 4167.
(22) Leading reference for coordination chemistry of phosphine chalco-
genides: Hartley, F. R. The Chemistry of Organophosphorus Com-
pounds; John Wiley & Sons Ltd.: New York, 1992; Chapter 8.
(23) Burford, N.; Royan, B. W.; Spence, R. E. v. H.; Cameron, T. S.;
Linden, A.; Rogers, R. D. J. Chem. Soc., Dalton Trans. 1990, 1521.
(b) Burford, N.; Royan, B. W.; Spence, R. E. V. H.; Rogers, R. D. J.
Chem. Soc., Dalton Trans. 1990, 2111.
Complex 7 crystallized in the highly symmetric space group
P21/n. Selected bond distances and angles are given in Table
(19) A representation of complex 6 is contained in the Supporting
Information, R ) 0.127.
(20) Winter, C. H.; Sheridan, P. H.; Lewkebandara, T. S.; Heeg, M. J.;
Proscia, J. W. J. Am. Chem. Soc. 1992, 114, 1095. (b) McKarns, P.
J.; Yap, G. P. A.; Rheingold, A. L.; Winter, C. H. Inorg. Chem. 1996,
35, 5968. (c) Mimoun, H.; Postel, M.; Casabianca, F.; Fischer, J.;
Mitschler, A. Inorg. Chem. 1982, 21, 1303. (d) Postel, M.; Casabianca,
F.; Gauffreteau, Y.; Fischer, J. Inorg. Chim. Acta 1986, 113, 173. (e)
Winter, C. H.; Lewkebandara, T. S.; Proscia, J. W.; Rheingold, A. L.
Inorg. Chem. 1994, 33, 1227.
(24) The sum of the covalent radii of Ti and O (1.98-2.05 Å) and Ti and
P (2.38 Å): (a) Porterfield, W. W. Inorganic Chemistry, 2nd ed.;
Academic Press: San Diego, CA, 1998; p 214. (b) Jolly, W. L. Modern
Inorganic Chemistry; McGraw-Hill: New York, 1984; p 52.
(25) For a theoretical treatment of diatomic ligand coordination modes to
transition metals: (a) Hoffmann, R.; Chen, M. M. L.; Thorn, D. L.
Inorg. Chem. 1977, 16, 503. (b) Mealli, C.; Hoffmann, R.; Stockis,
A. Inorg. Chem. 1984, 23, 56.

Synthesis and Structure of trans-(TTP)Ti[OP(Oct)3]2
Inorganic Chemistry, Vol. 40, No. 3, 2001 503
Table 3. Atom and Group Transfer Reactions Utilizing
(TTP)Ti(η2-3-hexyne)
bond cleavage
bond strength
(kcal/mol)
reagent
by 1a
(CH3)2SdO
Ph2SdO
yesb
87c
89c
yesb
(MeO)2SdO
(tolyl)2OSdO
Ph3PdO
yesd
116c
113c
128e
133f
nob
nod
tBuNCdO
tBuNdCO
Ph3AsdO
tBuNCdS
Ph3PdS
no (CdO)d
yes (NdC)d
nod
103g
71h
yesd
yesi
88j
Cy3PdS
yesd
98j
Figure 2. Magnetic moment vs temperature plot for complex 7.
SCdS
yesd
103c
tBuNCdSe
Ph3PdSe
yesd
the limiting phosphonium representation, R3P+-O-.27 A waving
distortion28 is observed in the deviations from the mean plane
containing the 24-atom porphyrin core and titanium [Ti (0), N1
(3), N2 (-16), C1 (-5), C2 (-5), C3 (3), C4 (6), C5 (8), C6
(-5), C7 (1), C8 (1), C9 (-5), C10 (7 pm)]. Although there
are no short intermolecular contacts, the waving distortion and
relatively small Ti-O-P angle may result from the bulky OP-
(Oct)3 groups. Two of the octyl groups extend linearly and lie
in a coplanar manner to the porphyrin. The third octyl group
achieves similar spacing relative to the porphyrin by rotation
around the C33-C34 bond. The pyrrole nitrogen, N2 is eclipsed
by the Ti-O-P unit. Since the Ti-O1 vector cants toward
N2A, N2 is displaced out of the porphyrin plane toward O1.
The variable temperature magnetic behavior found for
complex 7 is displayed in Figure 2. At 296 K the magnetic
moment is 1.60 µB and falls smoothly to 0.25 µB at 41 K. This
behavior is analogous to that of (TTP)Ti(4-picoline)2.4a These
values are much lower than the spin-only value of 2.83 µB for
two unpaired electrons.
yesi
67j
40l
(TMS)N-N2
iPrNCdNiPr
yesk
yesd
a Reactions were performed at 20 °C in C6D6 and monitored by 1H
NMR unless otherwise indicated. b Reference 4b. c Reference 31e.
d This work. e Reference 31c. f Value for MeNCdO, ref 31e. g Refer-
ence 31d. h Value for MeNCdS, ref 31e. i Reference 4a. j Reference
t
31a. k Reference 10. l Value for BuN-N2, ref 31b.
Attempts at establishing absolute values for the Ti-alkyne
bond strengths by monitoring thermal ligand dissociation in
solution 1H NMR spectroscopy were unsuccessful. The 1H NMR
signals of (TTP)Ti(η2-3-hexyne) broadened irreversibly into the
baseline upon heating to 373 K, precluding quantification of
the species in solution. For (TTP)Ti(η2-PhCtCPh), no dis-
sociation was observed up to 373 K. Thus, a lower estimate of
the Ti-alkyne bond energy is g12 kcal/mol as no dissociation
was observed.30 With this Ti-alkyne bond strength and
tabulated bond strengths for small molecules (Table 3),31
estimates of the TidX bond strengths were determined for
(TTP)TidX (X ) O, S, Se, NR). Cleavage of the sulfur-oxygen
double bond in dimethyl sulfite requires 116 kcal/mol. With
the estimated bond energy of the Ti-alkyne fragment, a TidO
bond strength of g128 kcal/mol is obtained. In comparison,
theoretically and thermochemically derived TidO bond strengths
are 143 kcal/mol32 and 146 kcal/mol [TiO2(g)].33 Furthermore,
Ti-O single bond energies have been found to range from 89
to 115 kcal/mol.34 On the basis of the sulfur atom abstraction
between 1 and Cy3PdS, a TidS bond strength of g110 kcal/
mol is calculated. Selenium atom transfer between Ph3PdSe
and 1 provides a lower limit to the TidSe bond of 79 kcal/
mol. Similarly, nitrene group transfer from RNCO to 1 involves
cleavage of the nitrogen-carbon double bond, which requires
≈88 kcal/mol. Thus, the titanium-nitrogen bond energy in
(TTP)TidNR is g100 kcal/mol.
Discussion
Group and Atom Transfer Reactions. The porphyrin
macrocycle serves as a robust framework for studying group
and atom transfer reactions of transition metal complexes.29 This
is particularly true in cases where multielectron redox processes
are involved. The porphyrin ligand prevents severe structural
reorganizations that typically accompany large changes in formal
metal oxidation states. Our development of low-valent Ti
porphyrin complexes, (TTP)Ti(η2-alkyne), has been very useful
in this regard. The Ti(II) complex is an extremely potent
reductant and a versatile atom acceptor reagent. In an extension
of our previous atom transfer work, we have examined the
chemistry of (TTP)Ti(η2-3-hexyne) with heterocumulenes. New
reactions described in this work provide alternate synthetic
methods for preparing Ti(IV) complexes in addition to providing
a means of estimating TidX multiple bond strengths. It should
be noted that the atom/group transfer reactions here were not
inhibited by the presence of added 3-hexyne.
Although similar atom and group transfer reactions were
found with compounds 6 and 7, these reactions required heating.
(30) This estimate is conservatively low based on the barrier to rotation of
four electron donor alkyne ligands. Alt, H. G.; Engelhardt, H. E. Z.
Naturforsch., B: Anorg. Chem., Org. Chem. 1985, 40B (9), 1134, and
references therein.
(26) OdP(C6H11)3, 1.490(2) Å; Davies, J. A.; Dutremez, S.; Pinkerton, A.
A. Inorg. Chem. 1991, 30, 2380. (b) OdP(CH3)3, 1.489(6) Å;
Engelhardt, L. M.; Raston, C. L.; Whitaker, C. R.; White, A. H. Aust.
J. Chem. 1986, 39, 2151. (c) OdP(CH2CH2CN)3, 1.498(3) Å; Cotton,
F. A.; Darensbourg, D. J.; Fredrich, M. F.; Ilsley, W. H., Troup, J. M.
Inorg. Chem. 1981, 20, 1869.
(31) Capps, K. B.; Wixmerten, B.; Bauer, A.; Hoff, C. D. Inorg. Chem.
1998, 37, 2861. (b) Claydon, A. P.; Fowell, P. A.; Mortimer, C. T. J.
Chem. Soc. 1960, 3284. (c) Hudson, R. F. Structure and Mechanism
in Organo-Phosphorus Chemistry; Academic Press: London, 1965.
(d) Barnes, D. S.; Burkinshaw, P. M.; Mortimer, C. T. Thermochim.
Acta 1988, 131, 107. (e) Benson, S. W. Chem. ReV. 1978, 78, 23.
(32) Fisher, J. M.; Piers, W. E.; Ziegler, T.; MacGillivray, L. R.; Zaworotka,
M. J. Chem. Eur. J. 1996, 2, 1221.
(27) Chesnut, D. B.; Savin, A. J. Am. Chem. Soc. 1999, 121, 2335, and
references therein.
(28) Jentzen, W.; Simpson, M. C.; Hobbs, J. D.; Song, X.; Ema, T.; Nelson,
N. Y.; Medforth, C. J.; Smith, K. M.; Veyrat, M.; Mazzanti, M.;
Ramasseul, R.; Marchon, J.-C.; Takeuchi, T.; Goddard, W. A., III.;
Shelnutt, J. A. J. Am. Chem. Soc. 1995, 117, 11085.
(33) Glidewell, C. Inorg. Chim. Acta 1977, 24, 149.
(34) (a) Lappert, M. F.; Patil, D. S.; Pedley, J.B. J. Chem. Soc., Chem.
Commun. 1975, 830. (b) Ziegler, T.; Tschinka, V.; Versluis, L.;
Baerends, E. J.; Ravenek, W. Polyhedron 1988, 7, 1625. (c) Dias, A.
R.; Martinho Simoes, J. A. Polyhedron 1988, 7, 1531.
(29) Woo, L. K. Chem. ReV. 1993, 93, 1125.

504 Inorganic Chemistry, Vol. 40, No. 3, 2001
Thorman et al.
Table 4. Metrical Parameters for Selected Atom Transfer Partners
Ti-N (average)/Å
Ti-Cta
(OEP)Ti(η2-Et-C≡C-Et)
(OEP)TidO
2.094b
0.54b
2.114c
0.603(6)c
S-C/Å
C-S-C/deg
Me2SdO
Me2S
Ph2SdO
(p-MeC6H5)2S
1.80d
1.82e
1.76d
1.75e
97.3d
105.0e
97.3d
Figure 3. Bonding modes of isocyanates.
109.0e
THF with picoline. The triethylphosphine ligands in complex
6 are rapidly displaced by pyridine and OP(Oct)3. Treatment
of complex 6 with excess diphenylacetylene produced an
equilibrium mixture of the diamagnetic monoacetylene complex,
(TTP)Ti(η2-PhCtCPh), and complex 6 (K ∼ 0.2). Further
variable temperature analysis of this equilibrium was prevented
by decomposition of the Ti(II) complexes to uncharacterized,
NMR-silent products. In the presence of excess pyridine, the
trioctylphosphine oxide ligands in complex 7 are only partially
displaced to form a mixed species, (TTP)Ti[OP(Oct)3](py).
There is a contrasting ability to displace 3-hexyne from
complex 1 with OP(Ph)3 compared to the phosphate OP(OPh)3.
The phosphine oxide completely displaces the alkyne ligand
within minutes. Treatment of compound 1 with the phosphate
results in no displacement, even at 80 °C. This can be attributed
to the less nucleophilic character of the phosphate.37 Likewise,
the phosphine imine, Et3PdNSiMe3, undergoes no reaction with
complex 1.
P-C/Å
C-P-C/deg
Ph3PdS
Ph3P
Cy3PdS
Cy3P
1.817f
105.7f
102.0g
108.0f
103.8g
1.83g
1.839f
1.868g
a Ti displacement out-of-mean porphyrin plane. b Reference 45.
c Reference 46. d Reference 47. e Reference 48. f Reference 49. g Ref-
erence 26a.
For example, formation of (TTP)TidN(SiMe3) from treatment
of complex 7 with N3(SiMe3) required heating the reaction
mixture to 60 °C. In contrast, the facile reaction between the
alkyne adduct, 1, and N3(SiMe3) occurred at ambient temper-
ature. Heating a solution of the bis(phosphine) species, 6, in
the presence of dimethyl sulfite produced (TTP)Ti(OMe)2,9
(TTP)TidO, and Et3PdS.
Attempts at oxygen atom abstraction from CO2, (PhO)3PO,
(Et2N)3PO, and Ph3PO were unsuccessful despite the ability of
low-valent Ti(II) complexes to break such strong bonds.35 The
reverse reaction, oxygen atom transfer from (TTP)TidO to
tBuNC, POct3, PPh3, or P(OPh)3, was also not observed. Use
of diphenylacetylene or pyridine to trap the reactive (TTP)Ti-
(II) intermediate also failed to promote atom transfer. Clearly,
a kinetic barrier must exist in the spontaneous direction for these
oxygen atom transfer couples.
In the above atom transfer analysis for TidX bond strengths,
the issue of reorganization energies should be addressed. Table
4 lists metrical parameters of selected atom transfer partners
for comparison. Because X-ray structures for (TTP)TidO and
(TTP)Ti(η2-RCtCR) are unknown, structural parameters for
octaethylporphyrin analogues are presented. Metrical parameters
for (TTP)TidS and (TTP)TidSe are also unknown. From the
data in Table 4, it is clear that the reduced and oxidized Ti
porphyrin complexes have very similar Ti-N distances and Ti
out-of-plane displacements. Also, oxygen abstraction from
sulfoxides results in small changes in S-C bond distances (∆
) 0.02 Å) and C-S-C angles (∆ ) 8°-12°). Similarly,
phosphine sulfides and the corresponding phosphines have very
similar P-C bond lengths and C-P-C angles. Consequently
reorganization energies for atom transfer reactions involving
these species are likely to be small. Nonetheless, the bond
strengths determined above must still be considered as rough
estimates.
Atom Transfer Intermediates. The binding of heterocumu-
lenes to mid- and late-transition metals has been well estab-
lished.38 However, isolable examples of early-transition metal-
heterocumulene complexes are rare. Known low-valent metal
complexes include examples of η1-CO2, η2-CO2, η2-CS2, and
t
η2-RNCNR.39 The reaction between 1 and BuNCdCh (Ch )
S, Se) yields a diamagnetic, short-lived species observed by
NMR. This transient compound possesses a nine-proton singlet
at -0.52 ppm, which is assigned to a tBu group of a coordinated
ligand. Because the chalcogenido complexes, (TTP)TidCh, do
not bind additional donor ligands, it does not seem likely that
this intermediate is a simple isocyanide or isochalcogocyanate
adduct of the terminal chalcogenido compound. Moreover,
t
t
(TTP)TidCh, free BuNC, and BuNCdCh are quantitatively
accounted for in the 1H NMR spectrum. Likewise, the 3-hexyne
is accounted for as either bound (-0.12 (q), -0.87 (t)) or free
(2.05 (q), 1.00 (t)). Thus, it is reasonable to assign this
intermediate as a titanium complex containing only one bound
tBuNCdCh, structure A, B, or C (Figure 3). Given the
(37) The phosphate is expected to have a smaller cone angle than the that
of phosphine oxide. Dias, P. B.; Minas de Piedade, M. E.; Martinho
Simoes, J. A. Coord. Chem. ReV. 1994, 135, 737.
(38) Rosi, M.; Sgamellotti, A.; Tarantelli, F.; Floriani, C. Inorg. Chem.
1987, 26, 3805, and references therein. (b) Gibson, J. A. E.; Cowie,
M. Organometallics 1984, 3, 984.
(39) Jegat, C.; Fouassier, M.; Tranquille, M.; Mascetti, J. Inorg. Chem.
1991, 30, 1529. (b) Baird, M. C.; Hartwell, G.; Wilkinson, G. J. Chem.
Soc. A 1967, 2037. (c) Pasquali, M.; Gambarotta, S.; Floriani, C.;
Chiesa-Villa, A.; Guastini, C. Inorg. Chem. 1981, 20, 165. (d)
Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, G. J. Am.
Chem. Soc. 1985, 107, 2985. (e) Carmona, E.; Munoz, M. A.; Peraz,
P. J.; Poveda, M. L. Organometallics 1990, 9, 1337. (f) Bristow, G.
S.; Hitchcock, P. B.; Lappert, M. F. J. Chem. Soc., Chem. Commun.
1981, 1145. (g) Cenini, S.; La Monica, G. Inorg. Chim. Acta 1976,
18, 279. (h) Gambarotta, S.; Fiallo, M. L.; Floriani, C.; Chiesa-Villa,
A.; Guastini, C. Inorg. Chem. 1984, 23, 3532. (i) Fachinetti, G.; Biran,
C.; Floriani, C.; Chiesa-Villa, A.; Guastini, C. Inorg. Chem. 1978,
11, 2995. (j) Antinolo, A.; Carillo-Hermosilla, F.; Otero, A.; Fajardo,
M.; Garces, A.; Gomez-Sal, P.; Lopez-Mardomingo, C.; Martin, A.;
Miranda, C. J. Chem. Soc., Dalton Trans. 1998, 59.
Ligand Exchange Reactions. The reported ligand exchange
reactions of titanocene and bis(pentadienyl) titanium(II) deriva-
tives have dealt largely with CO and phosphines.5,36 The system
in this work has made use of a wide variety of axial donor
ligands. The metalloporphyrin fragment (TTP)Ti(II) has a
preference for strong σ-donors, exhibited by displacement of
(35) Fachinetti, G.; Floriani, C.; Chiesta-Villa, A.; Guastini, C. J. Am. Chem.
Soc. 1979, 101, 1767. (b) Mathey, F.; Maillet, R. Tetrahedron Lett.
1980, 21, 2525.
(36) Fryzuk, M. D.; Haddad, T. S.; Berg, D. J. Coord. Chem. ReV. 1990,
99, 137.

Synthesis and Structure of trans-(TTP)Ti[OP(Oct)3]2
Inorganic Chemistry, Vol. 40, No. 3, 2001 505
Figure 4. Fit of data to model with a ground state singlet and excited
triplet state at 576 cm-1, 0.3% of paramagnetic impurity (S ) 1) and
a constant amount added to the susceptibility (0.0005 cgsu).
diamagnetism of the intermediate and its subsequent conversion
to terminal sulfido and selenido products, the η2-bound form B
may be the most likely formulation. The reaction of 1 with
RNCO produces an imido product. Thus, form C is the most
likely intermediate for the alkyl isocyanate adduct. The forma-
tion of terminal chalcogenido complexes, (TTP)TidCh, from
RNCS and RNCSe rather than imido production can be traced
to weaker CdCh bonds relative to the CdN bond.
Magnetic Properties of Complex 7. The temperature-
dependent magnetic susceptibility of complex 7 is shown in
Figure 4. The susceptibility falls with decreasing temperature
to near diamagnetism and then increases sharply at liquid helium
temperatures. The magnetic moment for this complex at room
temperature, ≈1.6 µB, is significantly lower than that for a triplet,
S ) 1, ground state expected for an octahedral d2 titanium(II)
complex of 2.83 µB. This moment falls rapidly to ≈0.25 µB at
liquid helium temperatures.
There appears to be two possible explanations for this
behavior. Either the complex has a diamagnetic S ) 0 ground
state with a thermally accessible excited triplet state or there is
a spin equilibrium involving an S ) 0 and an S ) 1 state.
Attempts to fit the temperature variation of the magnetic moment
in terms of a ground state singlet and thermally accessible triplet
state with the inclusion of a small amount of a paramagnetic
impurity gave qualitative agreement with the observed data.
However, the main discrepancy between the calculated and
observed regions of the fit was in the “diamagnetic” region
between 40 and 150 K where the difference, 500 × 10-6 cgsu,
is of the same order of magnitude as the diamagnetic corrections
for the sample. An excellent fit to the data could be obtained
by the addition of this quantity to the model. This gave a ground-
state singlet with excited triplet state at 576 cm-1 and 0.3% of
paramagnetic impurity (S ) 1) (Figure 4). This additional
temperature-independent contribution to the susceptibility may
well be due in part to contributions from second-order Zeeman
(temperature-independent paramagnetism) effects. These would
normally be expected to be smaller (<100 × 10-6 cgsu) for
titanium(II) complexes; however, the close proximity of the
singlet and triplet states may give rise to a larger effect.
Figure 5. Calculated structure for Ti(porphine)[OP(CH3)3]2.
(S ) 0). The calculated structure was in good agreement with
that determined for complex 7 (Figure 5). The Ti-O and P-O
bond lengths were calculated to be 2.10 and 1.53 Å, respectively,
in comparison to the measured values of 2.080 and 1.513 Å.
The Ti-O-P angle was calculated to be 141.7° (average)
compared to the X-ray value of 138.43°. A Mulliken population
analysis gave charges of 1.78, -0.85, and 0.87 for the Ti, O,
and P atoms. This is consistent with the R3P+-O- representation
of the coordinated phosphine oxide. The Ti d orbital population
was found to be 2.03.
With the molecular geometry calculated for the singlet state,
the energy of the lowest lying triplet state was calculated to be
only 0.19 kcal/mol higher in energy. Thus, the singlet and triplet
states in this molecular geometry are nearly degenerate.
Examination of the frontier orbitals showed the HOMO to be
composed of a titanium dxz orbital antibonding with respect to
an O pπ orbital of the phosphine oxide and one component of
the porphyrin eg (π) molecular orbital. The Ti dxz orbital was
also a component of other lower lying occupied molecular
orbitals. The LUMO and LUMO+1 consist mainly of the Ti
dxy and dyz orbitals, respectively (Figure 6). All three of these
orbitals are nearly degenerate.
These calculations support the conclusion drawn from the
magnetic properties of complex 7, which show the ground state
to be a spin singlet in close proximity to a triplet state. The
nature of the ground state of complex 7 is counter to that
expected from Hund’s rules. The three “t2g” titanium orbitals
are nearly degenerate yet the singlet state is the lowest. There
are two reports relevant to this observation: (1) The diamag-
netism of the titanium(II) complex Ti(dppe)2Me2 reported by
Girolami et al.40 and (2) the observation of a singlet ground
2-
state with a thermally accessible triplet state in the C60
dianion.41 In the first complex, the interelectron interaction has
been reduced such that pairing of electrons in a lower energy
titanium orbital gives a lower energy singlet state42 while in
the second system there is formally a triply degenerate set of
Electronic Structure Calculations for Complex 7. Insight
into the electronic structure of this complex was facilitated by
computations using density functional theory. A full geometry
optimization with no symmetry restraints was performed on the
molecule Ti(porphine)[(OP(CH3)3)]2 as a model for complex
7. It was assumed that the electronic ground state was a singlet
(40) Jensen, J. A.; Wilson, S. R.; Schultz, A. J.; Girolami, G. S. J. Am.
Chem. Soc. 1987, 109, 8094.
(41) Boyd, P. D. W.; Bhyrappa, P.; Paul, P.; Stinchcombe, J.; Bolskar, R.;
Sun. Y.; Reed. C. A. J. Am. Chem. Soc. 1995, 117, 2907.

506 Inorganic Chemistry, Vol. 40, No. 3, 2001
Thorman et al.
spin on the â carbons atoms. This observation is well-known
in the NMR spectra of paramagnetic iron porphyrins.43 In the
intermediate spin iron(III) porphyrins, which have singly
occupied dxz and dyz orbitals, similar upfield shifts are observed.44
Conclusion
The Ti(II) complex, (TTP)Ti(η2-3-hexyne), 1, is a potent
reductant and a versatile inner-sphere acceptor reagent. Treat-
ment of complex 1 with a variety of heterocumulenes such as
RNdCO, iPrNdCNiPr, CS2, tBuNCdS, and tBuNCdSe results
in group or atom transfer and formation of the multiply bonded
species (TTP)TidNR, (TTP)TidS, or (TTP)TidSe. In addition,
complex 1 abstracts an oxygen from (MeO)2SdO to produce
(TTP)TidO. These reactions were useful in determining esti-
mates for TidO, TidS, TidSe, and TidNR bond strengths.
Notably, complex 1 does not abstract oxygen from Od
P(Oct)3. Instead, simple substitution occurs to produce the bis-
ligand adduct (TTP)Ti[OP(Oct)3]2, 7. Density functional cal-
culations indicate that the magnetic properties of this complex
arise from a ground state singlet state with a thermally accessible
triplet state.
Acknowledgment. We are grateful for support from the
Camille and Henry Dreyfus Foundation. We also thank Dr. Jerry
Ostenson for obtaining the SQUID data and Mr. Charles Baker
for the mass spectral data. P.D.W.B. is grateful to the University
of Auckland Research Committee for support.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of (TTP)Ti[OdP(Oct)3]
and (TTP)Ti(PEt3)2. This material is available free of charge via the
Internet at http://pubs.acs.org.
Figure 6. Bonding and frontier orbitals for Ti(porphine)[OP(CH3)3]2:
(a) Ti(d)-O (pπ) bonding, (b) Ti(dxz)-O (pπ) bonding, (c) HOMO Ti-
(dxz), (d) LUMO Ti(dxy), and (e) LUMO+1 Ti(dyz).
IC0003426
(43) Iron Porphyrin: Part 1; Lever, A. B. P., Gray, H. B., Ed.; Addison-
Wesley: Reading, MA, 1983.
(44) Goff, H.; Shimomura, E. J. Am. Chem. Soc. 1980, 102, 31.
(45) Woo, L. K.; Hays, J. A.; Jacobson, R. A.; Day, C. Organometallics
1991, 10, 2102.
(46) Guilard, R.; Latour, J.-M.; Lecomte, C.; Marchon, J.-C.; Protas, J.;
Ripoll, D. Inorg. Chem. 1978, 17, 1228.
(47) Oae, S. Organic Sulfur Chemistry: Structure and Mechanism; CRC
Press: Boca Raton, FL, 1991; p 69.
(48) Gilheany, D. G. In The Chemistry of Organophosphorus Compounds;
Hartley, F. R., Ed.; John Wiley: New York, 1992; Vol. 2.
(49) Maier, L. In Organic Phosphorus Compounds; Kosolapoff, G. M.,
Maier, L., Eds.; John Wiley: New York, 1972; Vol. 1, Chapter 1, p
95.
highly delocalized molecular orbitals. The observed behavior
in complex 7 appears more like the second case.
The observed chemical shifts of the porphyrin â pyrrole
protons at -33.0 ppm are in keeping with the nature of the
occupied orbitals in the thermally accessible triplet state, which
are the titanium dxz and dyz orbitals that mix with the porphyrin
eg molecular orbitals, allowing delocalization of the unpaired
(42) Simpson, C. Q.; Hall, M. B.; Guest, M. F. J. Am. Chem. Soc. 1991,
113, 2898.