Phosphoramidite complexes of Pd(II), Pt(II) and Rh(I): An effective hydrosilylation catalyst of 1-hexyne and 1-octene

Article abstract of DOI:10.1016/j.ica.2017.04.065

The hydrophosphorane HP(OC₆H₄NMe)₂ was used to prepare the diastereotopic complexes [MCl₂{P(OC₆H₄NMe)OC₆H₄NHMe}] (M?=?Pd, Pt) by reaction with [MCl₂(PhCN)₂], and [RhCl(PPh₃){P(OC₆H₄NMe)OC₆H₄NHMe}] by reaction with [RhCl(PPh₃)₃]. To form these complexes, the phosphorane undergoes ring-opening, whereby it is coordinated as the tautomeric neutral phosphoramidite-amino chelating ligand. The crystal structure of [RhCl(PPh₃){P(OC₆H₄NMe)OC₆H₄NHMe}] was determined and the geometry about the Rh(I) atom is square-planar with cis-disposed phosphorus-donor ligands. The Rh–P distance is shortened (2.1056(6) ?) due to Rh(d)?→?P π-backbonding. In addition, [RhCl(PPh₃){P(OC₆H₄NMe)OC₆H₄NHMe}] was shown to be an effective regio- and stereoselective catalyst for the hydrosilylation of 1-octene and 1-hexyne.

Full text of DOI:10.1016/j.ica.2017.04.065

Accepted Manuscript
Research paper
Phosphoramidite Complexes of Pd(II), Pt(II) and Rh(I): An Effective Hydrosi-
lylation Catalyst of 1-Hexyne and 1-Octene
Hannah K. Carroll, Fraser G.L. Parlane, Noah Reich, Benson J. Jelier, Craig D.
Montgomery
PII:
S0020-1693(17)30193-7
http://dx.doi.org/10.1016/j.ica.2017.04.065
ICA 17610
DOI:
Reference:
Inorganica Chimica Acta
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Accepted Date:
17 February 2017
11 April 2017
12 April 2017
Please cite this article as: H.K. Carroll, F.G.L. Parlane, N. Reich, B.J. Jelier, C.D. Montgomery, Phosphoramidite
Complexes of Pd(II), Pt(II) and Rh(I): An Effective Hydrosilylation Catalyst of 1-Hexyne and 1-Octene, Inorganica
Chimica Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.04.065
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Phosphoramidite Complexes of Pd(II), Pt(II) and Rh(I): An Effective
Hydrosilylation Catalyst of 1-Hexyne and 1-Octene
Hannah K. Carrolla, Fraser G.L. Parlanea,c, Noah Reicha, Benson J. Jelierb,d, Craig D.
Montgomerya*,
Dept. of Chemistry, Trinity Western University, 7600 Glover Road, Langley, B.C., V2Y 1Y1
Canada
(*for corresponding author: phone: (604) 513-2121 ext. 3210 fax: (604) 513-2018 e-mail:
montgome@twu.ca)
Dept. of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, B.C., V5A 1S6
Canada
a Trinity Western University
b
Simon Fraser University
c Current address: Department of Chemistry, UBC Faculty of Science, 2036 Main Mall,
Vancouver, B.C., Canada V6T 1Z1
d Current address: Laboratorium für Anorganische Chemie, ETH Zürich,Vladimir-Prelog Weg
2, 8093 Zürich, Switzerland

2
Phosphoramidite Complexes of Pd(II), Pt(II) and Rh(I): An Effective
Hydrosilylation Catalyst of 1-Hexyne and 1-Octene
Hannah Carrolla, Fraser G.L. Parlanea, Noah Reicha, Benson J. Jelierb, Craig D. Montgomerya*,
Abstract
The hydrophosphorane HP(OC6H4NMe)2 was used to prepare the diastereotopic complexes
[MCl2{P(OC6H4NMe)OC6H4NHMe}] (M = Pd, Pt) by reaction with [MCl2(PhCN)2], and
[RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}] by reaction with [RhCl(PPh3)3]. To form these
complexes, the phosphorane undergoes ring-opening, whereby it is coordinated as the tautomeric
neutral phosphoramidite-amino chelating ligand. The crystal structure of
[RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}] was determined and the geometry about the Rh(I)
atom is square-planar with cis-disposed phosphorus-donor ligands. The Rh-P distance is
shortened (2.1056(6) Å) due to Rh(d)ꢀP π-backbonding. In addition,
[RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}] was shown to be an effective regio- and
stereoselective catalyst for the hydrosilylation of 1-octene and 1-hexyne.
Key words: hydrosilylation; phosphoramidite; homogeneous catalysis; diastereomers

3
Graphical Abstract
The rhodium(I) complex [RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}] was shown to be an
effective catalyst for the hydrosilylation of 1-octene and 1-hexyne with various hydrosilanes.

4
1. Introduction
Hydrophosphoranes (HPR4) have been increasingly employed as ligands in coordination and
organometallic chemistry due to their unique binding modes and influence on catalytic activity.
These compounds have been used previously in the synthesis of metallophosphoranes (or
metalated phosphoranes) - pentacoordinate phosphorus compounds that include a phosphorus-
metal bond - by the deprotonation of the hydrophosphorane followed by metathesis with a
transition metal chloride [1-8]. Specifically, the hydrophosphorane HP(OC6H4NMe)2 L1 studied
herein, has been employed in this fashion [3], though complexes featuring the same
phosphoranide P(V) ligand have also been prepared by other routes [9-11].
Some spirobicyclic hydrophosphoranes exhibit an additional ring-opening tautomerism,
resulting in a P(III) species (Scheme 1) [12-17]. As a result, hydrophosphoranes have also been
used to prepare complexes featuring a P(III) ligand, either chelating or monodentate [18-20].
Scheme 1. Tautomerism of spirobicyclic hydrophosphoranes (E = O, NR).
Herein, we report the utilization of the HP(OC6H4NMe)2 in the ring-opened form, as a
chelating phosphoramidite-amine ligand in the synthesis of the diastereotopic complexes

5
[MCl2]{P(OC6H4NMe)OC6H4NHMe}] (M=Pd 1, Pt 2) and
[RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}] 3.
Catalytic hydrosilylation is a very important reaction in organosilicon chemistry, with
platinum and rhodium complexes frequently employed as catalysts [21-23]. Additionally, the
reactivity of hydrosilanes with transition metal complexes has been recently reviewed [24].
While recent hydrosilylation catalytic studies have successfully employed ONO-pincer ligands
[25], N-heterocyclic carbene (NHC) ligands [26-28], ionic liquids [29,30], as well as fluorous
biphase systems [31,32], nevertheless phosphorus ligands continue to be prove useful in these
catalytic systems [33]. Phosphoramidite ligands, and other P(III) ligands originating from
hydrophosphoranes, have been employed recently in a variety of catalysts, such as those for
Heck-coupling [20,34], hydroformylation [35], as well as pre-catalysts for Hiyama cross-
coupling [36] and co-catalysts for the oxidation of aldehydes [37]. Other phosphoramidite
ligands have been utilized in catalysts for enantioselective allylic substitution by Hartwig and
Carreira [38,39]. Herein, we report the ability of a diastereotopic Rh(I) phosphoramidite complex
to act as a catalyst for the hydrosilylation of terminal alkenes and alkynes, with high regio- and
stereoselectivity.
2. Experimental
2.1 General methods
All manipulations were performed under pre-purified nitrogen in a Vacuum Atmospheres
HE-493 glovebox equipped with a HE-493 purifier, or in standard Schlenk-type glassware.
Solvents were dried by refluxing over sodium benzophenone, followed by distillation under N2;
solvents were stored over sodium metal or 3Å molecular sieves. HP(OC6H4NCH3)2 L1 was

6
prepared by the literature method [15], as were [PtCl2(NCPh)2] and [PdCl2(PhCN)2] [40].
[[RhCl3(PPh3)3], 1-octene, and 1-hexyne along with the various silanes were purchased from
Sigma Aldrich. All NMR spectra were recorded on a Bruker WH-400 at spectrometer
31
frequencies of 400 MHz, 162 MHz and 86 MHz for H, P and 195Pt, and were referenced to
1
external TMS, H3PO4 and [K2PtCl6] respectively. Gas chromatography/mass spectrometry
(GC/MS) analyses employed an Agilent Technologies 6890N GC coupled with an Agilent
Technologies 7638B series injector and Agilent Technologies 5975B inert mass spectrometer
detector (MSD) with electron impact (EI) as the mode of ionization.
2.2 Synthesis of [PtCl2{P(OC6H4NMe)OC6H4NHMe}] (1)
HP(OC6H4NMe)2 (0.0500 g, 0.1823 mmol) was dissolved in THF (10 mL) and added
dropwise to a solution of [PtCl2(NCPh)2] (0.0861 g, 0.1823 mmol) in THF (50 mL). This
solution was then refluxed under nitrogen for 72 h. After cooling, the solution was filtered
through Celite under nitrogen. The addition of hexanes caused the product to precipitate as a
white powder. Yield = 91%. Anal. Calc. for C14H15Cl2N2O2PPt: C, 31.13; H, 2.80; N, 5.19;
Found: C, 31.75; H, 2.73; N, 5.11.
R,R/S,S-diastereomer: 1H NMR (400 MHz, CDCl3, δ ppm) 2.47 (d, 3J(1H,31P) = 12.1 Hz, 3H,
PNCH3), 2.55 (d, 3J(1H,1H) = 5.8 Hz, 3H, PtNCH3), 6.0 – 7.2 (br. m, 8H, OC6H4N); 31P{1H}
NMR (162 MHz, CDCl3, δppm) 89.8 (s 1J(31P,195Pt) = 6337 Hz,); 195Pt NMR (85.73 MHz,
CDCl3, δ ppm)) 3382 (d).
R,S/S,R-diastereomer: 1H NMR (400 MHz, CDCl3, δ ppm) 2.68 (d, 3J(1H,1H) = 5.8 Hz, 3H,
PtNCH3), 2.82 (d, 3J(1H,31P) = 12.3 Hz, 3H, PNCH3), 6.0 – 7.2 (br. m, 8H, OC6H4N); 31P{1H}
NMR (162 MHz, CDCl3, δppm) 88.7 (s 1J(31P,195Pt) 6345 Hz); 195Pt NMR (85.73 MHz, CDCl3,

7
δ ppm)) 3377 (d).
2.3 Synthesis of [PdCl2{P(OC6H4NMe)OC6H4NHMe}] (2)
HP(OC6H4NMe)2 (0.0500 g, 0.1823 mmol) was dissolved in THF (10 mL).
[PdCl2(NCPh)2] (0.0699 g, 0.1823 mmol) was likewise dissolved in THF (20 mL) and the two
solutions were combined and heated to 70 °C in a sealed vessel for 12 h. After cooling, the
solution was filtered through Celite under nitrogen and pumped to dryness. The product was
washed with hexanes (3 × 2 mL). Yield = 86.5%. Anal. Calc. for C14H15Cl2N2O2PPd: C, 37.24;
H, 3.35; N, 6.20; Found: C, 37.33; H, 3.04; N, 6.06.
R,R/S,S-diastereomer: 1H NMR (400 MHz, CDCl3, δ ppm) 3.231 (d, 3J(1H,31P) = 12.0 Hz, 3H,
PNCH3), 3.224 (d, 3J(1H,1H) = 6.0 Hz, 3H, PdNCH3), 6.41 (br. s, 1H, NH), 6.9 – 7.5 (br. m, 8H,
OC6H4N); 31P{1H} NMR (162 MHz, CDCl3, δ ppm) 114.0.
R,S/S,R-diastereomer: 1H NMR (400 MHz, CDCl3, δ ppm) 3.635 (d, 3J(1H,31P) = 12.8 Hz, 3H,
PNCH3), 3.220 (d, 3J(1H,1H) = 6.0 Hz, 3H, PdNCH3), 6.24 (br. s, 1H, NH), 6.9 – 7.5 (br. m, 8H,
OC6H4N); 31P{1H} NMR (162 MHz, CDCl3, δ ppm) 112.8.
2.4 Synthesis of [RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}] (3)
[RhCl(PPh3)3] (1.0000g, 0.5405 mmol) was dissolved in 10 mL of THF and HP(OC6H4NMe)2
(0.3230g, 0.9906 mmol) was dissolved in 5 mL of THF. The ligand solution was added to the
[RhCl(PPh3)3] solution and the resultant solution was heated to 70 °C in a sealed vessel for 88 h.
After heating, the solvent was removed with vacuum, forming a dark red oil. The oil was taken
up in a minimal amount of THF, and the dropwise addition of hexanes produced an orange

8
precipitate. The product was precipitated from THF/hexanes a second time. Yield = 81%. Anal.
(%) Calc. for C32H30ClN2O2P2Rh: C, 56.95; H, 4.48; N, 4.15; Found: C, 56.26; H, 4.47; N, 3.63.
R,R/S,S-diastereomer: 1H NMR (400 MHz, CDCl3, δ (ppm)) 2.88 (d, 3J(1H,31P) = 12.0 Hz, 3H,
PNCH3), 2.80 (d, 3J(1H,1H) = 8.0 Hz, 3H, RhNCH3), 5.49 (br. s, 1H, NH), 5.9 – 6.8 (br. m, 8H,
OC6H4N), 6.87 (br. m, 9H, P(C6H5) ortho, meta), 7.87 (br. m, 6H, P(C6H5) para); 31P{1H} NMR
(162 MHz, CDCl3, δppm) 146.6 (dd, 1J(31P,103Rh) = 322 Hz, 1J(31P,31P) = 64.8 Hz, PN2O2), 47.4
(dd, 1J(31P,103Rh) = 164 Hz, 1J(31P,31P) = 64.8 Hz, PPh3).
R,S/S,R-diastereomer: 1H NMR (400 MHz, CDCl3, δ ppm) 2.39 (d, 3J(1H,31P) = 12.0 Hz, 3H,
PNCH3), 2.89 (d, 3J(1H,1H) = 8.0 Hz, 3H, RhNCH3), 5.49 (br. s, 1H, NH), 6.9 – 7.5 (br. m, 8H,
OC6H4N); 31P{1H} NMR (162 MHz, CDCl3, δppm) 147.2 (dd, 1J(31P,103Rh) = 324 Hz,
1J(31P,31P) = 63.1 Hz, PN2O2), 47.6 (dd, 1J(31P,103Rh) = 164 Hz, 1J(31P,31P) = 63.1 Hz, PPh3).
2.5 X-ray Structure Determinations of [RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}] (3)
All diffraction data was collected using a Bruker SMART APEX II CCD area detector
diffractometer positioned 5.0 cm from the crystal with graphite monochromated Mo Kα
radiation (λ = 0.71073 Å). The frames were collected with a scan width of 0.5 in ω and were
integrated with the Bruker SAINT software. The structure was solved with the SIR92 [41]
structure solution program using Direct Methods and refined with the SHELXL-2013 [42]
refinement package using Least Squares minimization. In particular, a weighting function was
applied in the final cycles of least squares refinement of the form
2
2
w=1/[\ σ2(Fo )+(0.0407P)2+6.4756P] where P=(Fo +2Fc2)/3. All hydrogen atoms were placed
geometrically inferred from neighboring sites and treated by a mixture of independent and
constrained refinement. SADABS-2014/5 [43] was used for absorption correction where

9
wR2(int) was 0.0688 before and 0.0539 after correction. The ratio of minimum to maximum
transmission is 0.9123. Data collection: Bruker APEX2 [44]; cell refinement: CRYSTALS [45];
data reduction: Bruker SAINT [44]; program(s) used to solve structure: SIR92 [41]; program(s)
used to refine structure: SHELXL [46]; molecular graphics: OLEX2 [47]; software used to
prepare material for publication: OLEX2 [47]. A summary of crystal, data and refinement
parameters is provided in Table 1. Selected interatomic distances and angles appear in Table 2
and 3. Other tabulated data have been deposited which can be obtained, free of charge, via
http://www.ccdc.cam.ac.uk/products/csd/request/ [or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, U.K. (Fax: 44-1223-336033 or e-mail: deposit@
ccdc.cam.ac.uk)].
2.6 DFT Calculations
DFT geometry optimization calculations (B3LYP/6-31+G*) were carried out on both
[MCl2{P(OC6H4NMe)OC6H4NHMe}], M= Pt, (1); Pd, (2), as well as
[RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}] (3), using the SPARTAN 10 package. In addition, a
Spartan 16 DFT single point calculation (B3LYP/6-31+G*) was done on
[RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}] (3) using the atomic positions obtained from the
crystal structure determination.
2.7 Catalytic Hydrosilylations
In the glovebox, vials were charged with toluene (1mL), 1-octene or 1-hexyne (2 mmol),
the catalyst (3) (0.1 mol %), and one of four silanes (2.2 mol); triethoxysilane, triethylsilane,

10
ethyldimethylsilane, and dimethylphenylsilane. The vials were heated at a constant temperature
for 5 hours and analyzed via GC/MS with heptane was used as an internal standard.
Table 1 Crystal Data and Structure Refinement for 3.
Empirical formula
Formula weight
C36H38ClN2O3P2Rh
747.0
Temperature/K
149.99
Crystal system
monoclinic
Space group
P21/n
a/Å
13.8853(16)
b/Å
15.5710(18)
c/Å
16.1695(19)
α/°
90
β/°
103.270(2)
γ/°
90
3402.6(7)
Volume/Å3
Z
4
ρcalcg/cm3
1.456
0.713
µ/mm-1
F(000)
1532.0
0.5 × 0.5 × 0.5
MoKα (λ = 0.71073)
3.492 to 61.398
Crystal size/mm3
Radiation
2Θ range for data collection/°
Index ranges
-19 ≤ h ≤ 19, -21 ≤ k ≤ 22, -23 ≤ l ≤ 20
88113
10455 [Rint = 0.0509, Rsigma = 0.0326]
10455/0/408
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indexes [I>=2σ (I)]
Final R indexes [all data]
Largest diff. peak/hole / e Å-3
1.031
R1 = 0.0414, wR2 = 0.0934
R1 = 0.0623, wR2 = 0.1075
1.28/-0.77

11
3. Results and Discussion
3.1 Synthesis and Characterization of [MCl2{P(OC6H4NMe)OC6H4NHMe}], M= Pt, (1); Pd, (2)
Scheme 2. Synthesis of [MCl2{P(OC6H4NMe)OC6H4NHMe}], M = Pt, (1); Pd, (2).
Compounds 1 and 2 were synthesized as shown in Scheme 2 and were characterized by
1H and 31P NMR spectroscopy. In the case of the Pt(II) complex
[PtCl2{P(OC6H4NMe)OC6H4NHMe}] (1), the 31P{1H} NMR spectrum displayed two singlets,
each with 195Pt satellites. The appearance of two signals is explained by the fact that L1 has two
chiral centres (the coordinated P and N atoms) and thus would be expected to exist as two
diastereomers. These two diastereomers appear as a 52:48 ratio for the downfield (84.7 ppm):
upfield (83.9 ppm) signals.
Also of note in the 31P{1H} NMR spectrum are the very large 1J(31P,195Pt) values (6337 Hz
and 6345 Hz for the R,R/S,S and R,S/S,R diastereomers respectively). Likewise, the 195Pt NMR
displays two doublets at 3382 and 3377 ppm respectively for the two diastereomers, each with
the large 1J(31P,195Pt) coupling.
The 1H NMR is also consistent with this characterization. Each diastereomer gives rise to
two methyl proton signals, each a doublet; the protons of one methyl group (HNMe) are coupled
to the amine proton, while the other methyl proton (PNMe) signal is split into a doublet by

12
coupling to the 31P nucleus. These assignments were confirmed through decoupling experiments.
The Pd(II) complex [PdCl2L1] (2), exhibits similar spectra, also suggesting it exists as a
pair of diastereomers. The ratio of the two signals in the 31P{1H} NMR spectrum was similarly
53:47 in favour of the downfield signal. We were unsuccessful in separating the two
diastereomers through fractional reprecipitation in either the case of compound 1 or 2.
For both the Pt(II) complex 1 and the Pd(II) complex 2, computational studies were
undertaken and in each case, the calculations (B3LYP/6-31G*) produced optimized geometries
for both diastereomers; the two diastereomer models for 2 are shown in Fig. 1. The difference in
the two structures can be seen in the orientation of the two N-CH3 moieties with respect to each
other. In both cases, the calculations suggest that the R,R/S,S-diastereomer was favoured (by 27.0
kJ/mol for 1 and by 23.0 kJ/mol for 2). Likewise, the 31P{1H} NMR spectra of 1 and 2 show that
the ratio of the two diastereomers favoured the upfield signal. Tentative assignments of
diastereomers were made to the NMR spectra based upon the calculated energies. It is of note
that the DFT calculations suggest an energy difference that does not precisely match the
diastereomer ratios. One factor that may contribute to the difference between calculations and
observations, is the fact that the DFT studies are calculated for a single molecule whereas the
NMR studies are undertaken in solution. Nevertheless, the DFT studies do offer a prediction of
the more stable diastereomer, and may then be used for tentative assignments of the NMR
signals.
(a) R,R-
(b) R,S-

13
Fig. 1. Optimized geometries (B3LYP/6-31G*) for the R,R- diastereomer (a) and R,S
diastereomer (b) of [PdCl2(L1)] (2).
Spirobicylic hydrophosphoranes undergoing ring-opening to form P(III) ligands have
been reported previously, as in the complex [PdCl2P(OCH2CMe2NH)OCH2CMe2NH2] which
also contains a neutral chelating phosphoramidite-amine ligand. This complex was used as a
Heck coupling catalyst by Sizek et al [20].
3.2 Synthesis and Characterization of [RhCl(PPh3)(L1)] (3)
[RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}] (3) was prepared by the reaction of
HP(OC6H4NMe)2 with [RhCl(PPh3)3], as depicted in Scheme 3.

14
Scheme 3. Synthesis of [RhCl(PPh3)(L1)], (3).
The 31P{1H} NMR spectrum was consistent with the proposed structure. Two
diastereomers were observed in the 31P{1H} NMR spectrum in a ratio of 1.6:1, in favour of the
upfield signal. As before, DFT calculations allowed for an assignment of R,R/S,S as the more
favoured diastereomer. Each diastereomer displayed an ABX pattern giving a doublet of
doublets for both the phosphoramidite and triphenylphosphine 31P nuclei. This characterization
was further corroborated by the 1H NMR spectrum, which showed the hydrophosphorane
coordinated as the ring-opened chelating neutral P(III) phosphoramidite-amino ligand,
{P(OC6H4NMe)OC6H4NHMe}. In addition, the crystal structure of 3 was determined and is
shown in Fig. 2; Table 2 contains selected bond distances and angles. The geometry about the
Rh(I) atom is slightly distorted square-planar, with the triphenylphosphine ligand coordinated in
a position cis to the phosphoramidite. The bite angle of the chelating ligand is 91.36(7)° while
the P-Rh-P angle is 94.45(3)°, presumably due to steric interactions between the aromatic rings
of the phosphine and phosphoramidite ligands. The unit cell contained one non-coordinating
THF molecule for each molecule of 3.
Table 2 Selected bond lengths (Å) and bond angles (°) for 3
Bond
Distance (Å)
2.1057(7)
2.162(2)
Bonds
Angle (∘)
91.36(7)
94.45(3)
173.50(7)
174.79(3)
84.01(7)
90.31(2)
Rh(1) - P(1)
Rh(1) - N(1)
Rh(1) - P(2)
Rh(1) - Cl(1)
P(1) - O(1)
P(1) - O(3)
P(1) - N(2)
P(1) - Rh(1) - N(1)
P(1) - Rh(1) - P(2)
N(1) - Rh(1) - P(2)
P(1) – Rh(1)1 – Cl(1)
N(1) – Rh(1)1 – Cl(1)
P(2) – Rh(1)1 – Cl(1)
2.2287(7)
2.3648(7)
1.644(2)
1.662(2)
1.670(2)

15
O(1)
N(1)
O(2)
P(1)
Rh(1)
N(2)
Cl(1)
Fig. 2. (left) Thermal ellipsoids plot (drawn at 50% probability) of [RhCl(PPh3)(L1)]] (3) in
which hydrogen atoms have been omitted for clarity. (right) Calculated HOMO-2 indicating π-
backbonding (Rh(d)ꢀ (P-O) σ*).
Also of interest in the structure of 3, is the Rh-P(1) bond distance (2.1057(7) Å) in the
case of the phosphoramidite ligand; literature searches suggest that this is an extremely short Rh-
P distance. Previously Rovis et al. reported Rh-P(phosphoramidite) bond distances shortened
(2.2423(6) Å) due to π-backbonding (Rh(d)ꢀ(P-O)σ*) [48]. DFT calculations using the atomic
coordinates from the crystal structure of 3 also lent support for the presence of Rh(d)ꢀP π-
backbonding; Fig. 2 shows the HOMO-2 molecular orbital calculated for 3. Consistent with this
π-backbonding also being directed into the P-O σ* orbital is the long P-O bond length of
1.662(2) Å. Another factor for the enhanced π-backbonding in 3 is the fact that the ligand trans
to the phosphoamidite is a chloride as compared in to those complexes in ref. 48 which feature
an olefin trans to the phosphoramidite.
While considering the Rh-P(1) bond in 3, the large 1J(31P,103Rh) values of 322 Hz and

16
324 Hz in the R,R/S,S- and R,S/S,R-diastereomers respectively, are also of note. By comparison,
the Rh(I) phosphoramidite complex reported by Rovis et al, exhibited a 1J(31P,103Rh) value of
243 Hz [48]. Skarzynska reports Rh(I) phosphoramidite complexes with 1J(31P,103Rh) values
ranging from 243.4 to 287.9 Hz [35]. As mentioned above, compound 1 likewise exhibits large
1J(31P,195Pt) values (6337 Hz and 6345 Hz for the R,R/S,S and R,S/S,R diastereomers
respectively). By comparison, a Pt(II) phosphoramidite complex prepared by Gavrilov et al, had
a 1J(31P,195Pt) coupling constant of 5605 Hz [18]. Clearly HP(OC6H4NCH3)2 L1, is not only able
to serve as a good π-acceptor ligand, as demonstrated by the short Rh-P(1) bond lengths, but also
establishes strong σ-interaction in the Pt(II) and Rh(I) complexes (1 and 3 respectively), given
the comparatively large 1J values.
3.3 Catalytic Hydrosilylation Reactions
The complex [RhCl(PPh3)(L1)] (3) was employed as a catalyst in the hydrosilylation of
1-octene (Scheme 4) and 1-hexyne (Scheme 5) with various hydrosilanes, with the results
presented in Tables 3 and 4, respectively.
Table 3 Results of hydrosilylation of 1-octene catalyzed by 3.

17
Table 4 Results of hydrosilylation of 1-hexyne catalyzed by 3.
From Table 3, it is apparent that 3 does indeed act as a catalyst for the hydrosilylation of 1-

18
octene with HSiEtMe2, HSiMe2Ph and HSiEt3. Turnover frequencies (TOF) at 75°C for these
three silanes were 1000, 500, and 329 h-1 respectively.
Perhaps more significantly, the catalyst displayed a very high degree of regioselectivity in the
hydrosilylations of substrates HSiEtMe2, HSiMe2Ph and HSiEt3. While the β-product formed by
anti-Markovnikov addition is typically observed in the hydrosilylation of alkenes and alkynes,
the β/α ratio is notably high in this case with ratios of 94.4/0.063, 97.0/0 and 59.9/0.9 for
HSiEtMe2, HSiMe2Ph and HSiEt3 respectively. The more prominent competing product in this
case was not the α-product, but rather isomerization of the alkene to 2-, 3- or 4-octene. Likewise,
very little dehydrogenative silylation occurred for systems considered in this study.
While it can be difficult to find analogous rhodium catalytic systems in terms of substrate,
silane and temperature, two comparable studies can be considered. The first studied
hydrosilylation of 1-octene with HSiEt3 at 60°C using NHC-rhodium hydroxide catalysts [26],
and the second used catalytic RhCl(PPh3)3 at 90°C in polyethylene glycol-based ionic liquids
[49]. The NHC-rhodium hydroxide system had a TOF of 158 h-1, while the RhCl(PPh3)3 system
had a TOF of 359 h-1 (compared to 329 h-1 in our system). In the former case, the β/α ratio was
10.9 to 1, whereas in our system it was 66.6 to 1, although as noted previously our system did
result in an increased isomerization of the 1-octene.
Similarly, 3 was effective as a catalyst in the hydrosilylation of 1-hexyne, as TOF values
were again high. For the hydrosilylation of 1-hexyne with HSiEtMe2 and HSiMe2Ph, TOF values
at 75°C were 1000 and 974, respectively. The TOF was lower in the case of HSi(OEt)3 (165 h-1),
however the rhodium compound 3 did successfully serve as a hydrosilylation catalyst.
Once again, the observed β/α ratios were high (46, 43 and 16.7 for HSiEtMe2, HSiMe2Ph
and HSi(OEt)3 respectively. In addition, in the case of 1-hexyne, the β−product can exist with

19
either E or Z stereochemistry. The Z isomer is often the kinetically favoured product in rhodium-
catalyzed hydrosilylation of alkynes with HSiR3 (where R = alkyl, aryl), but mechanisms have
been proposed whereby isomerization to the thermodynamically preferred E isomer can occur
[50]. In this study, the Z/E ratio depended upon the silane employed, as has been observed
previously. For HSiEtMe2, HSiMe2Ph, and HSi(OEt)3, the Z/E ratios were respectively 2.4/1,
1/4.1 and 2.8/1. That is, in the case of HSiEtMe2 and HSi(OEt)3, the Z isomer is preferred,
whereas in the case of HSiMe2Ph the E isomer is the dominant product (presumably through a
mechanism by which isomerization can occur).
For purposes of comparison, [Rh4(CO)12] was used as a catalyst for the hydrosilylation of 1-
hexyne with HSiEtMe2 and HSiMe2Ph at 25°C [50]. TOF values were 8.3 and 27.8, β/α ratios
were 3.8 and 6.7, and the Z/E ratios were 1.1 and 2.2 respectively.
4. Conclusions
By preparing the diastereotopic complexes [MCl2{P(OC6H4NMe)OC6H4NHMe}] (M = Pd,
Pt) and [RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}], we have demonstrated the utility of
HP(OC6H4NMe)2 as a source of chelating phosphoramidite-amino ligands. Furthermore, the
complex [RhCl(PPh3){P(OC6H4NMe)OC6H4NHMe}] demonstrated that these chelating
phosphoramidite ligands exhibit significant promise in catalytic hydrosilylation of alkenes and
alkynes, with high regioselectivity and stereoselectivity.
5. Acknowledgements
The authors wish to acknowledge the financial support of the Natural Sciences and
Engineering Research Council of Canada, as well as Trinity Western University and Simon

20
Fraser University.
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