Chemistry - Determining the oxidation state of a bridging platinum complex
Solution 1:
For organometallic complexes it's often easier to throw the "more electronegative element" idea out entirely and focus on the characteristics of the ligands. This is what @andselisk's comment is referring to. Generally ligands are partitioned into two types, $\ce{L}$ and $\ce{X}$:
$\ce{L}$ refers to neutral ligands: for example $\ce{CO}$, phosphines, $\ce{H2O}$, alkenes (via the pi bond), ... and $\ce{SMe2}$ falls comfortably in this category.
$\ce{X}$ refers to anionic ligands: for example halides, hydroxide, azide, alkyl anions such as $\ce{Me}$, ...
Other ligands can be constructed as sums of these: so for example η4-butadiene would be $\ce{L2}$ (two pi bonds coordinating to the metal), an allyl group would be $\ce{LX}$ (one pi bond plus one anionic centre - ignore resonance), and so on.
The oxidation state of the metal, then, is simply the charge on the metal plus the number of X ligands. In this case each Pt centre is neutral, and has two L and two X ligands. That makes for a total oxidation state of +2.
As another example, the platinum in Zeise's salt has one L ligand (ethylene), three X ligands (chloride), and a negative charge: so its oxidation state is $-1 + 3 = +2$.
Of course, this method will fall apart very quickly when there are non-innocent ligands: $\ce{NO}$ and $\ce{O2}$ are the examples that come to mind, although there are many more. But for relatively simple complexes they suffice.
Solution 2:
There is a very similar molecule in the literature this has aryls instead of methyls. (MEYTEP)
M.A.C.Lacabra, A.J.Canty, M.Lutz, J.Patel, A.L.Spek, Huailin Sun, G.van Koten, Inorg.Chim.Acta, 2002, volume 327, page 15. In the Cambridge database this compound is considered as a Pt(II) compound in the paper.
We also have the dimethyl compound with bridging dimethyl sulfide ligands. (XOFNUB)
Datong Song, Suning Wang, J.Organomet.Chem., 2002, volume 648, page 302 which is the compound which the poster was asking about. In the Cambridge database this is considered as Pt(II). The authors regard it as being a Pt(II) compound.
I would vote for it being a Pt(II) compound as the methyl is likely to be an anionic ligand. But there is a big "but".
As it is an organometallic compound we need to be careful about oxidation state. In organometallic chemistry it is often possible to draw the same compound in two different ways with different oxidation states. For example ferrocene can be regarded as an Iron(II) compound with two anionic Cp ligands. As an alternative we can regard the iron as being in the zero oxidation state and the Cp ligands are neutral ligands. Sometimes in organometallic chemistry oxidation state becomes a bit of a joke at times.
Back to our Pt compound, if we consider the methyl ligands to be neutral then the Pt can be in the zero oxidation state the dimethyl sulfide is a ligand which can offer up a lone pair to a metal.