Ti(μ : η1,η1-OCMe2CH2PPh 2)3Rh has a cylindrically symmetric triple bond

Article abstract of DOI:10.1039/a704890d

The cylindrical symmetry of Ti(μ : η¹,η¹-OCMe₂CH₂-PPh ₂)₃Rh permits maximum Rh(d_π) → Ti(d/p_π) overlap, resulting in a 2.2142(11) A metal-metal triple bond.

Full text of DOI:10.1039/a704890d

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1
1
Ti(m:h ,h -OCMe2CH2PPh2)3Rh has a cylindrically symmetric triple bond
LeGrande M. Slaughter and Peter T. Wolczanski*
Cornell University, Baker Laboratory, Department of Chemistry, Ithaca, New York, USA 14853
1
1
The cylindrical symmetry of Ti(m:h ,h -OCMe2CH2-
weeks (sealed tube); (ii) reversible formation of a CO adduct,
1
1
PPh2)3Rh permits maximum Rh(dp) ? Ti(d/pp) overlap,
Ti(m:h ,h -OCMe2CH2Ph2P)3RhCO 4† was noted [n(CO)
1956 cm21] and (iii) within 12 h, 2 equiv. of HCl converted 3
to precursor 2, generating H2 and a significant amount of
impurities (ca. 50%) in the process.
resulting in a 2.2142(11) Å metal–metal triple bond.
Aspects of heterogeneous materials exhibiting the strong metal–
support interaction (SMSI)1 have been modeled by homoge-
neous systems,2–6 some containing M–MA bonds of disparate
metals.5,6 Previously, we conducted an X-ray structural study of
1
1
An X-ray crystallograpic investigation of Ti(m:h ,h -OC-
Me2CH2Ph2P)3Rh·0.5C7H8, 3·0.5C7H8, revealed a C3 sym-
metry for the O3TiRhP3 core of 3 [dihedral angle OTiRhPav
15.8(20)°] that is broken when the external framework is
included (Fig. 1). The OCCP bridge conformations adjust to
maximize the number of favourable edge-to-face phenyl–
phenyl interactions, thereby skewing the periphery.10 A dis-
torted trigonal monopyramidal geometry is evident for Rh, with
Ti positioned apically and P–Rh–P angles of 113.22(5),
120.59(5) and 124.18(5)° describing an equatorial plane
approximately perpendicular to the TiRh vector [Ti–Rh–P(1–3)
96.29(5), 89.72(5), 97.30(5)°]. The Ti center is roughly
tetrahedral [O–Ti–O 107.7(2), 109.8(2), 112.4(2)°; O–Ti–Rhav
108.9(5)°] and the titanium–oxygen [d(Ti–O)av 1.830(3) Å] and
rhodium–phosphine bond lengths [d(Rh–P)av 2.319(3) Å] are
normal.
1
1
5
Cp*Zr(m:h ,h -OCH2PPh2)2RhMe2 (Cp* = h -C5Me5) that
revealed a short 2.444(1) Å ZrRh bond which was evaluated via
extended Hu¨ckel molecular orbital (EHMO) calculations of an
appropriately configured model, Cp(HO)2ZrRh(PH3)2Me2.5
The metal–metal interaction, which is approximately 0.25 Å
shorter than the sum of Zr (1.454 Å) and Rh (1.252 Å) covalent
radii, was described in terms of a s bond and a Rh(dp) ? Zr(dp)
bond. While the geometry of the alkoxyalkylphosphine bridges
and the single critical p interaction resulted in a strong bond, at
least by bond length criteria, the low symmetry of the complex
prevented a second p interaction from being significant. As a
consequence, we turned our attention to the synthesis of a
cylindrically symmetric metal–metal bond in order to increase
and perhaps maximize the strength of p interactions between
group 4 and 9 metal centers.5,7,8
The titanium–rhodium bond distance of 2.2142(11) Å
characterizes an extremely short heterobimetallic metal–metal
bond. When compared to the sum of Ti (1.324 Å) and Rh
covalent radii, the 0.362 Å reduction in bond length represents
a large deviation (FSR = 0.860)11 that supports formulation of
a Ti·Rh bond comprised of one Ti(d/ps)–Rh(d/ps) and two
Rh(dp) ? Ti(dTpp) interactions. This appraisal is in accord
Treatment of TiCl4(thf)2 with
3 equiv. of LiOC-
4
Me2CH2PPh2 in benzene at 25 °C for 3 h afforded
(Ph2PCH2CMe2O)3TiCl 1† as a viscous, clear yellow oil in 80%
yield. Although 1 was typically contaminated with ca. 5%
HOCMe2CH2PPh2, this was of sufficient purity to continue.
Upon stirring a benzene solution of tris(alkoxyphosphine)-
titanium chloride 1 and 0.5 equiv. of [RhCl(cod)]29 for 24 h at
25 °C, a color change from yellow to deep red was noted, and
an amorphous red solid was isolated from hexane. The major
product displayed broad resonances in its 1H and 31P{1H} NMR
spectra at 23 °C in C6D6, the latter implying a 2 :1 ratio of
bound and free phosphines, while the 31P{1H} NMR spectrum
at 28 °C exhibited broad, complex multiplets at d 52.17 and
56.42 in a 2:1 ratio corresponding to bound phosphines. At
1
1
with our EHMO investivations of Cp*Zr(m:h ,h -
OCH2PPh2)RhMe2,5 and more recent Fenske–Hall calculations
PPh2
PPh2
Cl
O
Ti
1
1
280 °C, we postulate the complex as ClTi(m:h ,h -OC-
O
Me2CH2Ph2P)3RhCl (2, Scheme 1),† but suggest that dimeriza-
Ph2P
O
1
1
tion
to
[ClTi(OCMe2CH2Ph2P)(m:h ,h -OCMe2CH2-
Ph2P)2Rh]2(m-Cl)2 is plausible at room temperature. Re-
crystallization and chromatographic purification efforts failed,
and the chemical shifts attributed to impurities (ca. 20–25%
integrated intensity) were consistent with the formation of
various aggregates with bridging alkoxyalkylphosphines {i.e.
1
25 °C, 24 h
C6H6
+ 1/2 [RhCl(cod)2]
– cod
1
1
1
1
[TiCl(m:h ,h -OCMe2CH2Ph2P)2ClRh(m:h ,h -PPh2CH2-
CMe2O)]n}.
Since 2 or any oligomeric variant could be a useful precursor
to the desired heterobinuclear metal–metal bonded species, the
red powder was reduced with 2 equiv. of Na/Hg in thf for 10 h
at 25 °C. After separation from the salt and Hg, the resulting
red–orange solid was dissolved in thf and chromatographed on
basic alumina (activity I). The solid generated upon removal of
thf was dissolved in toluene (60 °C) and crystallized at 278 °C
to afford deep red Ti(m:h ,h -OCMe2CH2Ph2P)3Rh 3† as a
C7H8 solvate in 24% overall yield. Reactivity studies implicated
a robust titanium–rhodium bond: (i) no reaction with H2 (10
equiv.) was observed upon heating in C6D6 at 140 °C for 2
PPh2
Cl
PPh2
Rh
O
O
Na/Hg
Ti
Cl
Rh
Ti
thf, –2 NaCl
10 h, 25 °C
PPh2
PPh2
O
O
O
PPh2
O
PPh2
1
1
2
3
Scheme 1
Chem. Commun., 1997
2109

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(a)
C(84)
for experimental assistance in the X-ray crystallographic
study.
C(83)
C(54)
C(45)
C(44)
C(85)
C(53)
C(46)
C(65)
C(42)
C(55)
C(81)
C(82)
Footnotes and References
C(43)
C(41)
C(52)
C(86)
C(64)
C(56)
* E-mail: ptwz@cornell.edu
C(51)
P(1)
† Selected analytical data: 1 (C6D6), dH 1.46 (6 H, s, CH3), 2.63 (2 H, d, JPH
3.2 Hz, PCH2), 7.01–7.09 (6 H, m, Ph), 7.50 (4 H, td, J 7.5, 1.8 Hz, Ph); dC
32.08 (d, JPH 7.6 Hz, CH3), 45.70 (d, JPH 16.8 Hz, PCH2), 88.44 (d, JPH 18.3
Hz, OC), 129.04 (d, J 2.2 Hz, m-Ph), 129.12 (s, p-Ph), 133.75 (d, JPH 19.1
Hz, o-Ph), 140.44 (d, JPH 12.3 Hz, ipso-Ph); dP 224.19 (s). 2 (major, C6D6),
dH 1.64 (12 H, br s, CH3), 1.71 (6 H, br s, CH3), 2.77 (4 H, br d, JPH 10 Hz,
PCH2), 3.07 (2 H, br d, JPH 2 Hz, PCH2), 6.62–6.93 (12 H, m, Ph),
6.95–7.10 (6 H, m, Ph), 7.34–7.54 (8 H, m, Ph), 7.67–7.80 (4 H, m, Ph); dP
217.3 (1 P, br s, n1/2 450 Hz, free Ph2P), 48 (2 P, br s, n1/2 1300 Hz, bound
Ph2P); (280 °C, C7D8); dP 52.17 (2 P, br m, JRhP 200 Hz, bound Ph2P),
56.42 (1 P, br m, JRhP 180 Hz, bound Ph2P). 3 (C6D6), d 1.40 (18 H, s, CH3),
3.07 (6 H, br s, PCH2), 6.94–6.97 (18 H, m, Ph), 7.26 (12 H, m, Ph); dC
34.83 (s, CH3), 45.22 (dd, J 16.5, 8.8 Hz, PCH2), 77.96 (dd, J 3.8, 3.0 Hz,
OC), 128.32 (s, Ph), 128.51 (s, Ph), 133.17 (dd, J 10.7, 5.3, o-Ph), 141.76
(ddd, J 18.3, 11.1, 3.4, ipso-Ph); dP 24.13 (d, JRhP 208 Hz); UV–VIS (thf),
310 nm (e 12,100 dm3 mol21 cm21); Anal. Calc. for C48H54O3P3-
TiRh·0.5C7H8. C, 63.85; H, 6.03. Found: C, 63.45; H, 5.98%. 4 (C6D6) dH
1.31 (18 H, s, CH3), 3.53 (6 H, br s, PCH2), 6.92–7.11 (18 H, m, Ph),
7.48–7.68 (12 H, m, Ph); dP 17.6 (d, JRhP 177 Hz).
C(66)
C(61)
P(3)
C(63)
C(92)
C(93)
C(91)
C(96)
Rh
C(72)
C(14)
C(62)
C(32)
C(95)
C(94)
C(34)
C(13)
Ti
C(11)
C(12)
C(7
P(2)
C(71)
C(31)
O(1)
C(74)
O(3)
C(76)
C(75)
C(33)
C(24)
C(21)
O(2)
C(22)
C(23)
(b)
C(54)
C(53)
C(52)
C(13)
C(55)
C(12)
‡ Crystallograpic data: 3·0.5C7H8: monoclinic, space group P21/c,
a = 13.899(2), b = 14.527(2), c = 24.016(3) Å, b = 96.040(10)°,
U = 4822.2(11) Å3, Z = 4, T = 293(2) K, m = 0.648 mm21, 6308
independent reflections, R1 = 0.0783, wR2 = 0.1297. CCDC 182/612.
C(51)
C(56)
C(11)
C(14)
C(41)
C(42)
P(1)
C(84)
C(43)
C(76)
C(46)
C(45)
C(32)
C(81)
C(44)
O(1)
C(8
C(83)
C(82)
C(86)
C(31)
C(75)
Rh
1 Strong Metal–Support Interactions, ed. R. T. K. Baker, S. J. Tauster and
J. A. Dumesic, ACS Symp. Ser. 298, American Chemical Society,
Washington, DC, 1986; S. J. Tauster, Acc. Chem. Res., 1987, 20, 389.
2 G. S. Ferguson and P. T. Wolczanski, Organometallics, 1985, 4,
1601.
3 S. M. Baxter, G. S. Ferguson and P. T. Wolczanski, J. Am. Chem. Soc.,
1988, 110, 4231.
4 S. M. Baxter and P. T. Wolczanski, Organometallics, 1990, 9, 2498.
5 G. S. Ferguson, P. T. Wolczanski, L. Pa´rka´nyi and M. C. Zonnevylle,
Organometallics, 1988, 7, 1967.
O(3)
C(74)
Ti
C(71)
P(2)
C(73)
C(66)
C(33)
C(72)
P(3)
C(34)
O(2)
C(65)
C(24)
C(61)
C(64)
C(91)
C(92)
C(62)
C(63)
C(96)
C(21)
C(22)
C(93)
C(95)
C(94)
6 W. J. Sartain and J. P. Selegue, Organometallics, 1989, 8, 2153;
W. J. Sartain and J. P. Selegue, Organometallics, 1989, 6, 1812;
W. J. Sartain and J. P. Selegue, J. Am. Chem. Soc., 1985, 107, 5818.
7 S. Friedrich, H. Memmler, L. H. Gade, W.-S. Li, I. J. Scowen,
M. McPartlin and C. E. Housecroft, Inorg. Chem., 1996, 35, 2433;
S. Friedrich, L. H. Gade, I. J. Scowen and M. McPartlin, Organome-
tallics, 1995, 14, 5344; S. Friedrich, L. H. Gade, I. J. Scowen and
M. McPartlin, Agnew. Chem., Int. Ed. Engl., 1996, 35, 1338.
8 D. Selent, R. Beckhaus and J. Pickardt, Organometallics, 1993, 12,
2857; G. Schmid, B. Stutte and R. Boese, Chem. Ber., 1978, 111,
1239.
1
1
Fig.
1
Side (a) and Ti–Rh parallel (b) views of Ti(m:h ,h -OC-
Me2CH2PPh2)3Rh 3. Selected (see text) interatomic distances (Å) and
angles (°): Ti–Rh 2.2142(11), Ti–O(1) 1.833(4), Ti–O(2) 1.831(4), Ti–O(3)
1.827(4), Rh–P(1) 2.318(2), Rh–P(2) 2.316(2), Rh–P(3) 2.322(2); O(1)–Ti–
Rh 109.5(1), O(2)–Ti–Rh 108.5(1), O(3)–Ti–Rh 108.9(1), Ti–O(1)–C(11)
143.8(3), Ti–O(2)–C(21) 137.9(4), Ti–O(3)–C(31) 144.1(3), O(1)–C(11)–
Cav 108.3(14), O(2)–C(21)–Cav 109.0(25), O(3)–C(31)–Cav 108.4(12),
(O)C–C–Pav 117.3(25), O(1)–Ti–Rh–P(1) 17.5(2), O(2)–Ti–Rh–P(2)
13.7(2), O(3)–Ti–Rh–P(3) 16.2(2).
9 G. Giordano and R. H. Crabtree, Inorg. Synth., 1990, 28, 88.
10 C. A. Hunter, Chem. Soc. Rev., 1994, 23, 101; C. A. Hunter and
J. K. M. Sanders, J. Am. Chem. Soc., 1990, 112, 5525.
11 F. A. Cotton and R. A. Walton, Multiple Bonds Between Metal Atoms,
Oxford University Press, New York, 2nd edn., 1993; L. Pauling, The
Nature of the Chemical Bond, Cornell University Press, Ithaca, NY,
1960.
on models of {MeC(CH2NSiMe3)3}MFe(CO)2Cp (M = Ti, Sn)
by Gade and coworkers.7 While it is difficult to assess the
influence of the alkoxyalkylphosphine bridges on d(Ti–Rh),
none of the bond angles and distances are characteristically
strained while imparting the desired cylindrical symmetry.
We thank the National Science Foundation and Cornell
University for support of this research, and Emil B. Lobkovsky
Received in Bloomington, IN, USA, 9th July 1997; 7/04890D
2110
Chem. Commun., 1997