I've heard claims that Indo-Europeans introduced things such as the wheel, chariots, and advanced metallurgy to the Chinese in the pre-Shang dyansty era. Some even claim that Indo-Europeans founded either the Shang or Zhou dyansties, and that modern Chinese are unrelated to them. I know at least the second one is a fringe theory at best, but is there any basis to either of these claims? If not, how would one counter them?
The wheeled vehicle and the chariot were almost certainly introduced into China by Indo-Europeans. The chariot appears in China about 1200BC, at about the same time that chariots - used by chariot warriors speaking Indo-European languages - appeared in Greece, in Mesopotamia, in northern India. We don't know what language the chariot warriors who drove chariots into China spoke, but they came from the steppe which was Indo-European dominated, and it is almost certain that these chariot warriors were Indo-European. That they spoke an Indo-European language is further suggested by Indo-European elements in Early Old Chinese as it appears in Shang oracle bone inscriptions (Beckwith 2009). As Beckwith notes,
The Early Old Chinese language of the Oracle Bone Inscriptions is either a non-Indo-European language with an intrusive Indo-European element or an Indo-European language with an intrusive non-Indo-European element.
As for advanced metallurgy, the evidence is less clear. Bronze technology came into China from the steppe, but there is no evidence that it came with people from the steppe (that is, the idea moved, rather than peoples moving). The claim that advanced metallurgy (which appears to mean bronze forging, as opposed to only casting) is an Indo-European introduction is based on pottery from Gansu which shows stylistic features common to some styles of Indo-European pottery. However, it seems that no "advanced" (i.e., forged bronze) objects have been found, and the evidence is poor at best (Pletcher 2011).
Iron working similarly appears to have come from the steppe, again without evidence of movement of peoples.
As for Indo-European origins of the Shang rulers, we find Indo-European style (i.e., steppe style) chariot burials in the Shang royal burial grounds (Beckwith 2009). Either the Shang rulers were of Indo-European origin, or partly of Indo-European origin and retained many elements of Indo-European culture, or were non-Indo-European but adopted many elements of Indo-European culture. The first of these three possibilities would be the case if the Shang were conquering invaders. The second could arise from a non-Indo-European ruling group allying with Indo-European chariot warriors (and adopting their military technology, inter-marrying, etc.). The linguistic evidence suggests that these two possibilities are more likely than the 3rd. (Note that the Tang brought in many Turkic elements, and inter-married with Turkic peoples; having a similar thing happen with the Shang is quite plausible.)
It doesn't follow that modern Chinese are unrelated to them, though.
At the very least, Indo-European peoples were next to China over this time - Indo-European peoples lived in the Tarim Basin by 2000BC, and spoke Indo-European languages (Tokharian) until the replacement of these languages by Turkic languages in the 9th century AD.
Reference:
Beckwith, Christopher I., Empires of the Silk Road: A History of Central Eurasia from the Bronze Age to the Present, Princeton University Press, 2009.
Kenneth Pletcher, The history of China, Britannica Educational Publishing, 2011.